draft-ietf-lisp-introduction-01.txt   draft-ietf-lisp-introduction-02.txt 
LISP Working Group J. N. Chiappa LISP Working Group J. N. Chiappa
Internet-Draft Yorktown Museum of Asian Art Internet-Draft Yorktown Museum of Asian Art
Intended status: Informational July 15, 2013 Intended status: Informational October 1, 2013
Expires: January 16, 2014 Expires: April 4, 2014
An Architecural Introduction to the LISP An Architectural Introduction to the LISP
Location-Identity Separation System Location-Identity Separation System
draft-ietf-lisp-introduction-01 draft-ietf-lisp-introduction-02
Abstract Abstract
LISP is an upgrade to the architecture of the IPvN internetworking LISP is an upgrade to the architecture of the IP internetworking
system, one which separates location and identity (currently system, one which separates location and identity (previously
intermingled in IPvN addresses). This is a change which has been intermingled in IP addresses). This is a change which has been
identified by the IRTF as a critically necessary evolutionary identified by the IRTF as a critically necessary evolutionary
architectural step for the Internet. In LISP, nodes have both a architectural step for the Internet. In LISP, nodes have both a
'locator' (a name which says _where_ in the network's connectivity 'locator' (a name which says _where_ in the network's connectivity
structure the node is) and an 'identifier' (a name which serves only structure the node is) and an 'identifier' (a name which provides a
to provide a persistent handle for the node). A node may have more persistent handle for the node). A node may have more than one
than one locator, or its locator may change over time (e.g. if the locator, or its locator may change over time (e.g. if the node is
node is mobile), but it keeps the same identifier. mobile), but it keeps the same identifier.
One of the chief novelties of LISP, compared to other proposals for One of the chief novelties of LISP, compared to other proposals for
the separation of location and identity, is its approach to deploying the separation of location and identity, is its approach to deploying
this upgrade. (In general, it is comparatively easy to conceive of this upgrade. LISP aims to achieve the near-ubiquitous deployment
new network designs, but much harder to devise approaches which will necessary for maximum exploitation of an architectural upgrade by i)
actually get deployed throughout the global network.) LISP aims to minimizing the amount of change needed (existing hosts and routers
achieve the near-ubiquitous deployment necessary for maximum can operate unmodified); and ii) by providing significant benefits to
exploitation of an architectural upgrade by i) minimizing the amount early adopters.
of change needed (existing hosts and routers can operate unmodified);
and ii) by providing significant benefits to early adopters.
This document is an introduction to the entire LISP system, for those This document is an introductory overview of the entire LISP system,
who are unfamiliar with it. for those who are unfamiliar with it. The first half of the document
is a unified stand-alone brief introduction to LISP, for those who
only want a basic understanding of LISP; the document taken as a
whole provides a more detailed overview of LISP and its operation.
Status of This Memo Status of This Memo
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Table of Contents Table of Contents
1. Prefaratory Note 1. Prefatory Note . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Background 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Deployment Philosophy 3. Deployment Philosophy . . . . . . . . . . . . . . . . . . . . 7
3.1. Economics 3.1. Economics . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Maximize Re-use of Existing Mechanism 3.2. Maximize Re-use of Existing Mechanism . . . . . . . . . . 8
3.3. 'Self-Deployment' 3.3. 'Self-Deployment' . . . . . . . . . . . . . . . . . . . . 8
4. LISP Overview 4. LISP Overview . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Basic Approach 4.1. Basic Approach . . . . . . . . . . . . . . . . . . . . . . 9
4.2. Basic Functionality 4.2. Basic Functionality . . . . . . . . . . . . . . . . . . . 10
4.3. Mapping from EIDs to RLOCs 4.3. Mapping from EIDs to RLOCs . . . . . . . . . . . . . . . . 11
4.4. Interworking With Non-LISP-Capable Endpoints 4.4. Interworking With Non-LISP-Capable Endpoints . . . . . . . 11
4.5. Security in LISP 4.5. Security in LISP . . . . . . . . . . . . . . . . . . . . . 12
5. Initial Applications 5. Initial Applications . . . . . . . . . . . . . . . . . . . . . 12
5.1. Provider Independence 5.1. Provider Independence . . . . . . . . . . . . . . . . . . 13
5.2. Multi-Homing 5.2. Multi-Homing . . . . . . . . . . . . . . . . . . . . . . . 13
5.3. Traffic Engineering 5.3. Traffic Engineering . . . . . . . . . . . . . . . . . . . 14
5.4. Routing 5.4. Routing . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.5. Mobility 5.5. Mobility . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.6. IP Version Reciprocal Traversal 5.6. IP Version Reciprocal Traversal . . . . . . . . . . . . . 15
5.7. Local Uses 5.7. Local Uses . . . . . . . . . . . . . . . . . . . . . . . . 16
6. Major Functional Subsystems 6. Major Functional Subsystems . . . . . . . . . . . . . . . . . 16
6.1. xTRs 6.1. xTRs . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1.1. Mapping Cache Performance 6.1.1. Mapping Cache Performance . . . . . . . . . . . . . . 17
6.2. Mapping System 6.2. The Mapping System . . . . . . . . . . . . . . . . . . . . 19
6.2.1. Mapping System Organization 6.2.1. Mapping System Organization . . . . . . . . . . . . . 19
6.2.2. Interface to the Mapping System 6.2.2. Interface to the Mapping System . . . . . . . . . . . 20
6.2.3. Indexing Sub-system 6.2.3. Indexing Sub-system . . . . . . . . . . . . . . . . . 21
7. Examples of Operation 7. Examples of Operation . . . . . . . . . . . . . . . . . . . . 23
7.1. An Ordinary Packet's Processing 7.1. An Ordinary Packet's Processing . . . . . . . . . . . . . 23
7.2. A Mapping Cache Miss 7.2. A Mapping Cache Miss . . . . . . . . . . . . . . . . . . . 24
8. Design Approach 8. Design Approach . . . . . . . . . . . . . . . . . . . . . . . 25
9. xTRs 9. Data Plane - xTRs . . . . . . . . . . . . . . . . . . . . . . 25
9.1. When to Encapsulate 9.1. When to Encapsulate . . . . . . . . . . . . . . . . . . . 25
9.2. UDP Encapsulation Details 9.2. UDP Encapsulation Details . . . . . . . . . . . . . . . . 26
9.3. Header Control Channel 9.3. Header Control Channel . . . . . . . . . . . . . . . . . . 27
9.3.1. Mapping Versioning 9.3.1. Mapping Versioning . . . . . . . . . . . . . . . . . . 27
9.3.2. Echo Nonces 9.3.2. Echo Nonces . . . . . . . . . . . . . . . . . . . . . 27
9.3.3. Instances 9.3.3. Instances . . . . . . . . . . . . . . . . . . . . . . 28
9.4. Probing 9.4. Probing . . . . . . . . . . . . . . . . . . . . . . . . . 28
9.5. Mapping Lifetimes and Timeouts 9.5. Mapping Lifetimes and Timeouts . . . . . . . . . . . . . . 29
9.6. Security of Mapping Lookups 9.6. Security of Mapping Lookups . . . . . . . . . . . . . . . 29
9.7. Mapping Gleaning in ETRs 9.7. Mapping Gleaning in ETRs . . . . . . . . . . . . . . . . . 30
9.8. Fragmentation 9.8. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 30
10. The Mapping System 10. Control Plane - The Mapping System . . . . . . . . . . . . . . 30
10.1. The Mapping System Interface 10.1. The Mapping System Interface . . . . . . . . . . . . . . . 31
10.1.1. Map-Request Messages 10.1.1. Map-Request Messages . . . . . . . . . . . . . . . . . 31
10.1.2. Map-Reply Messages 10.1.2. Map-Reply Messages . . . . . . . . . . . . . . . . . . 32
10.1.3. Map-Register and Map-Notify Messages 10.1.3. Map-Register and Map-Notify Messages . . . . . . . . . 32
10.2. The DDT Indexing Sub-system 10.2. The DDT Indexing Sub-system . . . . . . . . . . . . . . . 33
10.2.1. Map-Referral Messages 10.2.1. Map-Referral Messages . . . . . . . . . . . . . . . . 34
10.3. Reliability via Replication 10.3. Reliability via Replication . . . . . . . . . . . . . . . 34
10.4. Security of the DDT Indexing Sub-system 10.4. Security of the DDT Indexing Sub-system . . . . . . . . . 34
10.5. Extended Tools 10.5. Extended Tools . . . . . . . . . . . . . . . . . . . . . . 35
10.6. Performance of the Mapping System 10.6. Performance of the Mapping System . . . . . . . . . . . . 35
11. Deployment Mechanisms 11. Multicast Support in LISP . . . . . . . . . . . . . . . . . . 36
11.1. LISP Deployment Needs 11.1. Basic Concepts of Multicast Support in LISP . . . . . . . 36
11.2. Internetworking Mechanism 11.2. Initial Multicast Support in LISP . . . . . . . . . . . . 37
11.3. Proxy Devices 12. Deployment Issues and Mechanisms . . . . . . . . . . . . . . . 38
11.3.1. PITRs 12.1. LISP Deployment Needs . . . . . . . . . . . . . . . . . . 38
11.3.2. PETRs 12.2. Interworking Mechanism . . . . . . . . . . . . . . . . . . 38
11.4. LISP-NAT 12.2.1. Proxy Devices . . . . . . . . . . . . . . . . . . . . 39
11.5. Use Through NAT Devices 12.2.2. LISP-NAT . . . . . . . . . . . . . . . . . . . . . . . 40
11.5.1. First-Phase NAT Support 12.3. Use Through NAT Devices . . . . . . . . . . . . . . . . . 41
11.5.2. Second-Phase NAT Support 12.4. LISP and DFZ Routing . . . . . . . . . . . . . . . . . . . 41
11.6. LISP and DFZ Routing 12.4.1. Long-term Possibilities . . . . . . . . . . . . . . . 42
11.6.1. Long-term Possibilities 13. Fault Discovery/Handling . . . . . . . . . . . . . . . . . . . 42
12. Fault Discovery/Handling 13.1. Handling Missing Mappings . . . . . . . . . . . . . . . . 42
12.1. Handling Missing Mappings 13.2. Outdated Mappings . . . . . . . . . . . . . . . . . . . . 43
12.2. Outdated Mappings 13.2.1. Outdated Mappings - Updated Mapping . . . . . . . . . 43
12.2.1. Outdated Mappings - Updated Mapping 13.2.2. Outdated Mappings - Wrong ETR . . . . . . . . . . . . 43
12.2.2. Outdated Mappings - Wrong ETR 13.2.3. Outdated Mappings - No Longer an ETR . . . . . . . . . 43
12.2.3. Outdated Mappings - No Longer an ETR 13.3. Erroneous Mappings . . . . . . . . . . . . . . . . . . . . 44
12.3. Erroneous Mappings 13.4. Neighbour ETR Liveness . . . . . . . . . . . . . . . . . . 44
12.4. Neighbour Liveness 13.5. Neighbour ETR Reachability . . . . . . . . . . . . . . . . 44
12.5. Neighbour Reachability 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 45
13. Current Improvements 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
13.1. Improved NAT Support 16. Security Considerations . . . . . . . . . . . . . . . . . . . 46
13.2. Mobile Device Support 17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 46
13.3. Multicast Support 17.1. Normative References . . . . . . . . . . . . . . . . . . . 46
13.4. {{Any others?}} 17.2. Informative References . . . . . . . . . . . . . . . . . . 47
14. Acknowledgments Appendix A. Glossary/Definition of Terms . . . . . . . . . . . . 51
15. IANA Considerations Appendix B. Other Appendices . . . . . . . . . . . . . . . . . . 53
16. Security Considerations B.1. A Brief History of Location/Identity Separation . . . . . 53
17. References B.2. A Brief History of the LISP Project . . . . . . . . . . . 54
17.1. Normative References B.3. Old LISP 'Models' . . . . . . . . . . . . . . . . . . . . 55
17.2. Informative References B.4. The ALT Mapping Indexing Sub-system . . . . . . . . . . . 55
Appendix A. Glossary/Definition of Terms B.5. Early NAT Support . . . . . . . . . . . . . . . . . . . . 56
Appendix B. Other Appendices
B.1. Old LISP 'Models'
B.2. Possible Other Appendices
1. Prefaratory Note 1. Prefatory Note
This document is the first of a pair which, together, form what one This document is the first of a pair which, together, form what one
would think of as the 'architecture document' for LISP (the would think of as the 'architecture document' for LISP (the
'Location-Identity Separation Protocol'). Much of what would 'Location-Identity Separation Protocol'). Much of what would
normally be in an architecture document (e.g. the architectural normally be in an architecture document (e.g. the architectural
design principles used in LISP, and the design considerations behind design principles used in LISP, and the design considerations behind
various components and aspects of the LISP system) is in the second various components and aspects of the LISP system) is in the second
document, the 'Architectural Perspective on LISP' document. document, the 'Architectural Perspective on LISP' document.
This 'Architectural Introduction' document is primarily intended for This 'Architectural Introduction' document is primarily intended for
those who don't know anything about LISP, and want to start learning those who unfamiliar with LISP, and want to start learning about it.
about it. It is intended to both be easy to follow, and also to give It is intended to both be easy to follow, and also to give the reader
the reader a choice as to how much they wish to know about LISP. a choice as to how much they wish to know about LISP. Reading only
Reading only the first part(s) of the document will give a good high- the first part(s) of the document will give a good high-level view of
level view of the system; reading the complete document should the system; reading the complete document should provide a fairly
provide a fairly detailed understanding of the entire system. detailed understanding of the entire system.
This goal explains why the document has a somewhat unusual structure. This goal explains why the document has a somewhat unusual structure.
It is not a reference document, where all the content on a particular It is not a typical reference document, where all the content on a
topic is grouped in one place. (That role is filled by the various particular topic is grouped in one place. (That role is filled by
protocol specifications.) It starts with a very high-level view of the various protocol specifications.) Instead, it is structured as a
the entire system, to provide readers with a mental framework to help series of phases, each covering the entire system, but with
understand the more detailed material which follows. A second pass increasing detail.
over the whole system then goes into more detail; finally, individual
sub-systems are covered in still deeper detail. It starts with a very high-level view of the entire system, to
provide readers with a mental framework to help understand the more
detailed material which follows. A second pass over the whole system
then goes into more detail. Finally, individual sub-systems are
covered in still deeper detail.
The intent is two-fold: first, the multiple passes over the entire The intent is two-fold: first, the multiple passes over the entire
system, each one going into more detail, are intended to ease system, each one going into more detail, are intended to ease
understanding; second, people can simply stop reading when they have understanding; second, people can simply stop reading when they have
a detailed-enough understanding for their purposes. People who just a detailed-enough understanding for their purposes.
want to get an idea of how LISP works might only read the first
part(s), whereas people who are going to go on and read all the People who just want to get an idea of how LISP works might only read
protocol specifications (perhaps to implement LISP) would need/want the first two parts; they can stop reading either just before, or
to read the entire document. just after, Section 7, "Examples of Operation". People who are going
to go on and read all the protocol specifications (perhaps to
implement LISP) would need/want to read the entire document.
Note: This document is a descriptive document, not a protocol Note: This document is a descriptive document, not a protocol
specification. Should it differ in any detail from any of the LISP specification. Should it differ in any detail from any of the LISP
protocol specification documents, they take precedence for the actual protocol specification documents, they take precedence for the actual
operation of the protocol. operation of the protocol.
2. Background 2. Background
It has gradually been realized in the networking community that It has gradually been realized in the networking community that
networks (especially large networks) should deal quite separately networks, especially large networks, should deal quite separately
with the identity and location of a node (basically, 'who' a node is, with the 'identity' and 'location' of an 'endpoint' ([Chiappa]) -
and 'where' it is). At the moment, in both IPv4 and IPv6, addresses basically, 'who' an endpoint is, and 'where' it is. (A more detailed
indicate both where the named device is, as well as identify it for history of this evolution is in Appendix B.1, "A Brief History of
purposes of end-end communication. Location/Identity Separation".)
The distinction was more than a little hazy at first: the early
Internet [RFC791], like the ARPANET before it [Heart] [NIC8246], co-
mingled the two, although there was recognition in the early Internet
work that there were two different things going on. [IEN19]
This likely resulted not just from lack of insight, but also the fact
that extra mechanism is needed to support this separation (and in the
early days there were no resources to spare), as well as the lack of
need for it in the smaller networks of the time. (It is a truism of
system design that small systems can get away with doing two things
with one mechanism, in a way that usually will not work when the
system gets much larger.)
The ISO protocol architecture took steps in this direction [NSAP],
but to the Internet community the necessity of a clear separation was
definitively shown by Saltzer. [RFC1498] Later work expanded on
Saltzer's, and tied his separation concepts into the fate-sharing
concepts of Clark. [Clark], [Chiappa]
The separation of location and identity is a step which has recently At the moment, in both IPv4 and IPv6, IP addresses indicate both
been identified by the IRTF as a critically necessary evolutionary where the named node is, as well as identify it for purposes of end-
architectural step for the Internet. However, it has taken some time end communication. (The term 'node' is admittedly a nebulous one,
for this requirement to be generally accepted by the Internet but it was deliberately chosen for use in this document precisely
engineering community at large, although it seems that this may because its definition is not fixed, and therefore unlikely to cause
finally be happening. [RFC6115] erroneous images in the minds of readers. You will not go far wrong
if you think of a node as being something like a host.)
The LISP system for separation of location and identity resulted from However, the separation of location and identity is a step which has
the discussions of this topic at the Amsterdam IAB Routing and recently been identified by the IRTF as a critically necessary
Addressing Workshop, which took place in October 2006. [RFC4984] evolutionary architectural step for the Internet. [RFC6115]
A small group of like-minded personnel from various scattered The on-going LISP project is an attempt to provide a viable path
locations within Cisco, spontaneously formed immediately after that towards this separation. (A brief history of the LISP project can be
workshop, to work on an idea that came out of informal discussions at found in Appendix B.2, "A Brief History of the LISP Project".) As an
the workshop. The first Internet-Draft on LISP appeared in January, add-on to a large existing system, it has had to make certain
2007, along with a LISP mailing list at the IETF. [LISP0] compromises. (For a good example, see [Perspective], Section
"Residual Location Functionality in EIDs".) However, if it reaches
near-ubiquitous deployment, it will have two important consequences.
Trial implementations started at that time, with initial trial First, in effectively providing separation of location and identity,
deployments underway since June 2007; the results of early experience along with a distributed directory of the bindings between them,
have been fed back into the design in a continuous, ongoing process 'Wheeler's Law' ("All problems in computer science can be solved by
over several years. LISP at this point represents a moderately another level of indirection") will come into play, and the Internet
mature system, having undergone a long organic series of changes and technical community will have a new, immensely powerful, tool at its
updates. disposal. The fact that the namespaces on both sides of the mapping
are global ones maximizes the power of that tool. (See
[Perspective], Section "Need for a Mapping System", for more on
this.)
LISP transitioned from an IRTF activity to an IETF WG in March 2009, Second, because of combination of flexible capability built into
and after numerous revisions, the basic specifications moved to LISP, and the breaking of the unification of location and identity
becoming RFCs in 2012 (although work to expand and improve it names, further architectural evolvement of the Internet becomes
continues, and undoubtly will for a long time to come). easily available; for example, new namespaces for location could be
designed and deployed. (See [Future] for more on this.)
3. Deployment Philosophy 3. Deployment Philosophy
It may seem odd to cover 'deployment philosophy' at this point in It may seem odd to cover 'deployment philosophy' at this point in
such a document. However the deployment philosophy was a major such a document. However the deployment philosophy was a major
driver for much of the design (to some degree the architecture, and driver for much of the design (to some degree the architecture, and
to a very large measure, the engineering). So, as such an important to a very large measure, the engineering). So, as such an important
motivator, it is very desirable for readers to have this material in motivator, it is very desirable for readers to have this material in
hand as they examine the design, so that design choices that may seem hand as they examine the design, so that design choices that may seem
questionable at first glance can be better understood. questionable at first glance can be better understood.
Experience over the last several decades has shown that having a Experience over the last several decades has shown that having a
viable 'deployment model' for a new design is absolutely key to the viable 'deployment model' for a new design is absolutely key to the
success of that design. A new design may be fantastic - but if it success of that design. In general, it is comparatively easy to
can not or will not be successfully deployed (for whatever factors), conceive of new network designs, but much harder to devise approaches
it is useless. This absolute primacy of a viable deployment model is which will actually get deployed throughout the global network. A
what has lead to some painful compromises in the design. new design may be fantastic - but if it can not or will not be
successfully deployed (for whatever factors), it is useless.
The extreme focus on a viable deployment scheme is one of the This absolute primacy of a viable deployment model is what has lead
novelties of LISP. to some painful compromises in the design; and the extreme focus on a
viable deployment model (including economics) is one of the novelties
of LISP.
3.1. Economics 3.1. Economics
The key factor in successful adoption, as shown by recent experience The key factor in successful adoption, as shown by recent experience
in the Internet - and little appreciated to begin with, some decades in the Internet - and little appreciated to begin with, some decades
back - is economics: does the new design have benefits which outweigh back - is economics: does the new design have benefits which outweigh
its costs. its costs.
More importantly, this balance needs to hold for early adopters - More importantly, this balance needs to hold for early adopters -
because if they do not receive benefits to their adoption, the sphere because if they do not receive benefits to their adoption, the sphere
skipping to change at line 326 skipping to change at page 8, line 22
change to those that do, the lower the pain (and thus the greater the change to those that do, the lower the pain (and thus the greater the
likelihood) of deployment. likelihood) of deployment.
Designs which absolutely require 'forklift upgrades' to large amounts Designs which absolutely require 'forklift upgrades' to large amounts
of existing gear are far less likely to succeed - because they have of existing gear are far less likely to succeed - because they have
to have extremely large benefits to make their very substantial costs to have extremely large benefits to make their very substantial costs
worthwhile. worthwhile.
It is for this reason that LISP, in most cases, initially requires no It is for this reason that LISP, in most cases, initially requires no
changes to almost all existing devices in the Internet (both hosts changes to almost all existing devices in the Internet (both hosts
and routers); LISP functionality is needed in only a few places (see and routers); LISP functionality needs to be added in only a few
Section 11.1 for more). places (see Section 12.1, "LISP Deployment Needs", for more).
LISP also initially reuses, where-ever possible, existing protocols LISP also initially reuses, where-ever possible, existing protocols
(IPv4 [RFC791] and IPv6 [RFC2460]). The 'initially' must be stressed (IPv4 [RFC791] and IPv6 [RFC2460]). The 'initially' must be stressed
- careful attention has also long been paid to the long-term future - careful attention has also long been paid to the long-term future
(see [Future]), and larger changes become feasible as deployment (see [Future]), and larger changes become feasible as deployment
increases. increases.
3.3. 'Self-Deployment' 3.3. 'Self-Deployment'
LISP has deliberately employed a rather different deployment model, LISP has deliberately employed a rather different deployment model,
skipping to change at line 355 skipping to change at page 8, line 51
rolling a snowball down a hill: unless one starts with a big enough rolling a snowball down a hill: unless one starts with a big enough
snowball, and finds a hill of the right steepness (i.e. the right snowball, and finds a hill of the right steepness (i.e. the right
path for it to travel), one's snowball is not going to go anywhere on path for it to travel), one's snowball is not going to go anywhere on
its own. However, if one has picked one's spot correctly, once its own. However, if one has picked one's spot correctly, once
started, little additional work is needed. started, little additional work is needed.
4. LISP Overview 4. LISP Overview
LISP is an incrementally deployable architectural upgrade to the LISP is an incrementally deployable architectural upgrade to the
existing Internet infrastructure, one which provides separation of existing Internet infrastructure, one which provides separation of
location and identity. The separation is usually not perfect, for location and identity. It starts to separate the names used for
reasons which are driven by the deployment philosophy (above), and identity and location of nodes, which are currently unified in IPvN
explored in a little more detail elsewhere (in [Perspective], Section addresses. (This document uses the meaning for 'address' proposed in
"Namespaces-EIDs-Residual"). [Atkinson], i.e. a name with mixed location and identity semantics.)
LISP separates the functions of location and identity of nodes (a The separation into names with purely location and identity semantics
nebulous term, deliberately chosen for use in this document precisely is usually - but not necessarily - not perfect, for reasons which are
because its definition is not fixed - you will not go far wrong if driven by the deployment philosophy (above), and explored in more
you think of a node as being something like a host), which are detail elsewhere (in [Perspective], Section "Namespaces-EIDs-
currently intermingled in IPvN addresses. (This document uses the Residual").
meaning for 'address' proposed in [Atkinson], i.e. a name with mixed
location and identity semantics.)
4.1. Basic Approach 4.1. Basic Approach
In LISP, nodes have both a 'locator' (a name which says _where_ in In LISP, nodes have both an 'identifier' (a name which serves only to
the network's connectivity structure the node is), called an 'RLOC' provide a persistent handle for the node), called an 'EID' (short for
(short for 'routing locator'), and an 'identifier' (a name which 'endpoint identifier'), and an associated 'locator' (a name which
serves only to provide a persistent handle for the node), called an says _where_ in the network's connectivity structure the node is),
'EID' (short for 'endpoint identifier'). called an 'RLOC' (short for 'routing locator').
A node may have more than one RLOC, or its RLOC may change over time A node may be associated with more than one RLOC, or the RLOC may
(e.g. if the node is mobile), but it would normally always keep the change over time (e.g. if the node is mobile), but it would normally
same EID. always have the same EID.
Technically, one should probably say that ideally, the EID names the Ideally, one should think of the EID as naming the node - or rather,
node (or rather, its end-end communication stack, if one wants to be its end-end communication entity (see [Chiappa] for more), if one
as forward-looking as possible), and the RLOC(s) name interface(s). wants to be as forward-looking as possible. RLOC(s) name
(At the moment, in reality, the situation is somewhat more complex, interface(s) - usually on the xTRs, at this stage.
as will be explained elsewhere (in [Perspective], Section
"Namespaces-EIDs-Residual".)
This second distinction, of _what_ is named by the two classes of This second distinction, of _what_ is named by the two classes of
name, is necessary both to enable some of the capabilities that LISP name, is a further important enhancement to the architecture; failing
provides (e.g the ability to seamlessly support multiple interfaces, to clearly recognize interfaces, and end-end communication entities,
to different networks), and is also a further enhancement to the as distinctly separate classes of objects is another failing of the
architecture. Faailing to clearly recognize both interfaces and existing Internet architecture (again, one inherited from the
communication stacks as distinctly separate classes of things is previous generation of networking).
another failing of the existing Internet architecture (again, one
inherited from the previous generation of networking).
A novelty in LISP is that it uses existing IPvN addresses (initially, The distinction is also is necessary both to enable some of the
at least) for both of these kinds of names, thereby minimizing the capabilities that LISP provides (e.g the ability to seamlessly
deployment cost, as well as providing the ability to easily interact support multiple interfaces, to different networks).
with unmodified hosts and routers.
An important insight in LISP is that it initially uses existing IPvN
addresses for both of these kinds of names, as opposed to some
similar earlier proposals (e.g. [RFC1992]), which proposed using a
new namespace for locators. This choice minimized LISP's deployment
cost, as well as providing the ability to easily interact with un-
modified hosts and routers.
The capability to use other namespaces for both kinds of names is
already built in, which is expected to greatly increase the long-term
benefits, flexibility, and power of the LISP mapping layer.
4.2. Basic Functionality 4.2. Basic Functionality
The basic operation of LISP, as it currently stands, is that LISP The basic operation of LISP, as it currently stands, is quite simple.
augmented packet switches near the source and destination of packets LISP augmented packet switches near the source and destination of
intercept traffic, and 'enhance' the packets. packets intercept traffic, and 'enhance' the packets for the trip
between the LISP switches.
The LISP device near the source looks up additional information about The overall processing is shown below, in Figure 1:
the destination, and then wraps the packet in an outer header, one
which contains some of that additional information. The LISP device (to be added)
near the destination removes that header, leaving the original,
unmodified, packet to be processed by the destination node. Figure 1: Basic LISP Packet Flow
The LISP device near the original source (the Ingress Tunnel Router, The LISP device near the original source (the Ingress Tunnel Router,
or 'ITR') uses the information originally in the packet about the or 'ITR') looks up additional information about the destination, and
identity of its ultimate destination, i.e. the destination address, then wraps the packet in an outer header, one which contains some of
which in LISP is the EID of the ultimate destination. It uses the that additional information. The LISP device near the destination,
destination EID to look up the current location (the RLOC) of that the (the Egress Tunnel Router, or 'ETR') removes that header, leaving
EID. the original, un-modified, packet to be sent on to the destination
node.
To retrieve that additional information, the ITR uses the information
in the original packet about the identity of its ultimate
destination, i.e. the destination address; in LISP, this is the EID
of the ultimate destination. It uses the destination EID to look up
the current location (the RLOC) of that EID.
The lookup is performed through a 'mapping system', which is the The lookup is performed through a 'mapping system', which is the
heart of LISP: it is a distributed directory of mappings from EIDs to heart of LISP: it is a distributed directory of mappings from EIDs to
RLOCS. The destination RLOC will be (initially at least) the address RLOCs. The destination RLOC(s) will normally be the address(es) of
of the LISP device near the ultimate destination (the Egress Tunnel the ETR(s) near the ultimate destination.
Router, or 'ETR').
{{Is it worth distinguishing between 'mapping' and 'binding'? Should
the document pick one term, and stick with it?}}
The ITR then generates a new outer header for the original packet, The ITR then generates a new outer header for the original packet,
with that header containing the ultimate destination's RLOC as the with that header containing the ETR's RLOC as the wrapped packet's
wrapped packet's destination, and the ITR's own address (i.e. the destination, and the ITR's own address (i.e. the RLOC associated with
RLOC of the original source) as the wrapped packet's source, and the original source) as the wrapped packet's source, and sends it
sends it off. off.
When the packet gets to the ETR, that outer header is stripped off, When the packet gets to the ETR, that outer header is stripped off,
and the original packet is forwarded to the original ultimate and the original packet is forwarded to the original ultimate
destination for normal processing. destination for normal processing.
Return traffic is handled similarly, often (depending on the Return traffic is handled similarly, often (depending on the
network's configuration) with the original ITR and ETR switching network's configuration) with the original ITR and ETR switching
roles. The ETR and ITR functionality is usually co-located in a roles. The ETR and ITR functionality is usually co-located in a
single device; these are normally denominated as 'xTRs'. single device; these are normally denominated as 'xTRs'.
4.3. Mapping from EIDs to RLOCs 4.3. Mapping from EIDs to RLOCs
The mappings from EIDs to RLOCs are provided by a distributed (and The mappings from EIDs to RLOCs are provided by a distributed, and
potentially replicated) database, the mapping database, which is the potentially replicated, database, the 'mapping database', which is
heart of LISP. the heart of LISP. Entities which need mappings get them from the
'mapping system', which is a collection of subsystems through which
clients can find and obtain mappings. (The mapping system will be
discussed in more detail below, in Section 6.2, "The Mapping System"
and Section 10, "Control Plane - The Mapping System".)
Mappings are requested on need, not (generally) pre-loaded; in other Mappings are requested on demand, and generally not pre-loaded; in
words, mapping are distributed via a 'pull' mechanism. Once obtained other words, mappings are normally distributed via a 'pull'
by an ITR, they are cached by the ITR, to limit the amount of control mechanism. Once obtained by an ITR, they are cached by the ITR, for
traffic to a practicable level. (The mapping system will be performance reasons.
discussed in more detail below, in Section 6.2 and Section 10)
Extensive studies, including large-scale simulations driven by Extensive studies, including large-scale simulations driven by
lengthy recordings of actual traffic at several major sites, have lengthy recordings of actual traffic at several major sites, have
been performed to verify that this 'pull and cache' approach is been performed to verify that this 'pull and cache' approach is
viable, in practical engineering terms. (This subject will be viable, in practical engineering terms. (This subject will be
discussed in more detail in Section 6.1.1, below.) discussed in more detail in Section 6.1.1, "Mapping Cache
Performance", below.)
4.4. Interworking With Non-LISP-Capable Endpoints 4.4. Interworking With Non-LISP-Capable Endpoints
The capability for 'easy' interoperation between nodes using LISP, It is clearly crucial to provide the capability for 'easy'
and existing non-LISP-using hosts (often called 'legacy' hosts) or interoperation between hosts 'using' LISP (i.e. they are behind xTRs,
sites (where 'site' is usually taken to mean a collection of hosts, and their EIDs are in the mapping database), and existing non-LISP-
routers and networks under a single administrative control), is using hosts (often called 'legacy' hosts) or sites (where 'site' is
clearly crucial. usually taken to mean a collection of hosts, routers and networks
under a single administrative control).
To allow such interoperation, a number of mechanisms have been To allow such interoperation, a number of mechanisms have been
designed. This multiplicity is in part because different mechanisms designed. This multiplicity is in part because different mechanisms
have different advantages and disadvantages (so that no single have different advantages and disadvantages (so that no single
mechanism is optimal for all cases), but also because with limited mechanism is optimal for all cases); this also allows a choice to be
field experience, it is not clear which (if any) approach will be made when more field experience has been obtained.
preferable.
One approach uses proxy LISP devices, called PITRs (proxy ITRs) and One approach uses proxy LISP devices, called PITRs (proxy ITRs) and
PETRs (proxy ETRs), to provide LISP functionality during interaction PETRs (proxy ETRs), to provide LISP functionality during interaction
with legacy hosts. Another approach uses a device with combined LISP with legacy hosts. Another approach uses a device with combined LISP
and NAT ([RFC1631]) functionality, named a LISP-NAT. and NAT ([RFC1631]) functionality, named a LISP-NAT. (See
Section 12.2.1, "Proxy Devices", and Section 12.2.2, "LISP-NAT",
respectively, for details of each.)
4.5. Security in LISP 4.5. Security in LISP
LISP has a subtle security philosophy; see [Perspective], Section LISP has a subtle security philosophy; see [Perspective], Section
"Security", where it is laid out in some detail. "Security", where it is laid out in some detail.
To provide a brief overview, it is definitely understood that LISP To provide a brief overview, it is definitely understood that LISP
needs to be highly _securable_, especially in the long term; over needs to be highly _securable_, especially in the long term; over
time, the attacks mounted by 'bad guys' are becoming more and more time, the attacks mounted by 'bad guys' are becoming more and more
sophisticated. So LISP, like DNS, needs to be _capable_ of providing sophisticated. So LISP, like DNS, needs to be _capable_ of providing
'the very best' security there is. 'the very best' security there is.
At the same time, there is a conflicting goal: it must be deployable. At the same time, there is a conflicting goal: it must be deployable
That means two things: First, with the limited manpower currently (i.e. have a viable cost). That means two things: First, with the
available, we cannot expect to create the complete security apparatus limited manpower currently available, we cannot expect to create the
that we might see in the long term (which requires not just design, complete security apparatus that we might see in the long term (which
but also implementation, etc). Second, security needs to be requires not just design, but also implementation, etc). Second,
flexible, so that we don't overload the users with more security than security needs to be flexible, so that we don't overload the users
they need at any point. with more security than they need at any point.
To accomplish these divergent goals, the approach taken is to To accomplish these divergent goals, the approach taken is to
thorougly analyze what LISP needs for security, and then design, in thorougly analyze what LISP needs for security, and then design, in
detail, a scheme for providing that security. Then, steps can be detail, a scheme for providing that security. Then, steps can be
taken to ensure that the appropriate 'hooks' (such as packet fields) taken to ensure that the appropriate 'hooks' (such as packet fields)
are included at an early stage, when doing so is still easy. Later are included at an early stage, when doing so is still easy. Later
on, the design can be fully specified, implemented, and deployed. on, the design can be fully specified, implemented, and deployed.
LISP does already include a number of security mechanisms; in
particular, requesting mappings can be secured (see Section 9.6,
"Security of Mapping Lookups"), as can registering of xTRs (see
Section 10.1.3, "Map-Register and Map-Notify Messages"); the key
indexing database of the mapping system is also secured (see
Section 10.4, "Security of the DDT Indexing Sub-system").
The existing security mechanisms, and their configuration (which is
mostly manual at this point) currently in LISP are felt to be
adequate for the needs of the on-going early stages of deployment;
experience will indicate when improvements are required (within the
constraints of the conflicting goal given above).
5. Initial Applications 5. Initial Applications
As previously mentioned, it is felt that LISP will provide even the As previously mentioned, it is felt that LISP will provide even the
earliest adopters with some useful capabilities, and that these earliest adopters with some useful capabilities, and that these
capabilities will drive early LISP deployment. capabilities will drive early LISP deployment.
It is very imporant to note that even when used only for It is very imporant to note that even when used only for
interoperation with existing unmodified hosts, use of LISP can still interoperation with existing unmodified hosts, use of LISP can still
provide benefits for communications with the site which has deployed provide benefits for communications with the site which has deployed
it - and, perhaps even more importantly, can do so _to both sides_. it - and, perhaps even more importantly, can do so _to both sides_.
This characteristic acts to further enhance the utility for early This characteristic acts to further enhance the utility for early
adopters of deploying LISP, thereby increasing the cost/benefit ratio adopters of deploying LISP, thereby increasing the cost/benefit ratio
needed to drive deployment, and increasing the 'self-deployment' needed to drive deployment, and increasing the 'self-deployment'
aspect of LISP. aspect of LISP.
Note also that this section only lists likely _early_ applications Note also that this section only lists likely _early_ applications
and benefits - if and once deployment becomes more widespread, other and benefits - if and once deployment becomes more widespread, other
aspects will come into play (as described in [Perspective], in the aspects will come into play (as described in [Perspective], in the
"Goals of LISP" section). Section "Goals of LISP").
5.1. Provider Independence 5.1. Provider Independence
Provider independence (i.e. the ability to easily change one's Provider independence (i.e. the ability to easily change one's
Internet Service Provider) was probably the first place where the Internet Service Provider) was probably the first place where the
Internet engineering community finally really felt the utility of Internet engineering community finally really felt the utility of
separating location and identity. separating location and identity.
The problem is simple: for the global routing to scale, addresses The problem is simple: for the global routing to scale, addresses
need to be aggregated (i.e. things which are close in the overall need to be aggregated (i.e. things which are close in the overall
network's connectivity need to have closely related addresses), the network's connectivity need to have closely related addresses), the
so-called "provider aggregated" addresses. [RFC4116] However, if so-called "provider aggregatable" addresses. [RFC4116] However, if
this principle is followed, it means that when an entity switches this principle is followed, it means that when an entity switches
providers (i.e. it moves to a different 'place' in the network), it providers (i.e. it moves to a different 'place' in the network), it
has to renumber, a painful undertaking. [RFC5887] has to renumber, a painful undertaking. [RFC5887]
In theory, it ought to be possible to update the DNS entries, and In theory, it ought to be sufficient to update the DNS entries, and
have everyone switch to the new addresses, but in practise, addresses have everyone switch to the new addresses, but in practise, addresses
are embedded in many places, such as firewall configurations at other are embedded in many places, such as firewall configurations at other
sites. sites.
Having separate namespaces for location and identity greatly reduces Having separate namespaces for location and identity greatly reduces
the problems involved with renumbering; an organization which moves the problems involved with renumbering; an organization which moves
retains its EIDs (which are how most other parties refer to its retains its EIDs (which are how most other parties refer to its
nodes), but is allocated new RLOCs, and the mapping system can nodes), but is allocated new RLOCs, and the mapping system can
quickly provide the updated mapping from the EIDs to the new RLOCs. quickly provide the updated mapping from the EIDs to the new RLOCs.
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approach is to use provider-independent addressses - which moves the approach is to use provider-independent addressses - which moves the
problem into the global routing system, with attendant costs. This problem into the global routing system, with attendant costs. This
approach is also not really feasible for host multi-homing. approach is also not really feasible for host multi-homing.
Multi-homing was once somewhat esoteric, but a number of trends are Multi-homing was once somewhat esoteric, but a number of trends are
driving an increased desirability, e.g. the wish to have multiple ISP driving an increased desirability, e.g. the wish to have multiple ISP
links to a site for robustness; the desire to have mobile handsets links to a site for robustness; the desire to have mobile handsets
connect up to multiple wireless systems; etc. connect up to multiple wireless systems; etc.
Again, separation of location and identity, and the existince of a Again, separation of location and identity, and the existince of a
binding layer which can be updated fairly quickly, as provided by mapping layer which can be updated fairly quickly, as provided by
LISP, is a very useful tool for all variants of this issue. LISP, is a very useful tool for all variants of this issue.
5.3. Traffic Engineering 5.3. Traffic Engineering
Traffic engineering (TE) [RFC3272], desirable though this capability Traffic engineering (TE) [RFC3272], desirable though this capability
is in a global network, is currently somewhat problematic to provide is in a global network, is currently somewhat problematic to provide
in the Internet. The problem, fundamentally, is that this capability in the Internet. The problem, fundamentally, is that this capability
was not forseen when the Internet was designed, so the support for it was not forseen when the Internet was designed, so the support for it
via 'hacks' is neither clean, nor flexible. via 'hacks' is neither clean, nor flexible.
TE is, fundamentally, a routing issue. However, the current Internet TE is, fundamentally, a routing issue. However, the current Internet
routing architecture, which is basically the Baran design of fifty routing architecture, which is basically the Baran design of fifty
years ago [Baran] (a single large, distributed computationa), is ill- years ago [Baran] (a single large, distributed computation), is ill-
suited to provide TE. The Internet seems a long way from adopting a suited to provide TE. The Internet seems a long way from adopting a
more-advanced routing architecture, although the basic concepts for more-advanced routing architecture, although the basic concepts for
such have been known for some time. [RFC1992] such have been known for some time. [RFC1992]
Although the identity-location binding layer is thus a poor place, Although the identity-location mapping layer is thus a poor place,
architecturally, to provide TE capabilities, it is still an architecturally, to provide TE capabilities, it is still an
improvement over the current routing tools available for this purpose improvement over the current routing tools available for this purpose
(e.g. injection of more-specific routes into the global routing (e.g. injection of more-specific routes into the global routing
table). In addition, instead of the entire network incurring the table).
costs (through the routing system overhead), when using a binding
layer to provide TE, the overhead is limited to those who are In addition, instead of the entire network incurring the costs
actually communicating with that particular destination. (through the routing system overhead), when using a mapping layer to
provide TE, the overhead is limited to those who are actually
communicating with that particular destination.
LISP includes a number of features in the mapping system to support LISP includes a number of features in the mapping system to support
TE. (Described in Section 6.2 below.) TE. (described in Section 6.2, "The Mapping System", below); more
details about using LISP for TE can be found in [LISP-TE].
A number of academic papers have explored how LISP can be used to do Also, a number of academic papers have explored how LISP can be used
TE, and how effective it can be. See the online LISP Bibliography to do TE, and how effective it can be. See the online LISP
([Bibliography]) for information about them. Bibliography ([Bibliography]) for information about them.
5.4. Routing 5.4. Routing
Multi-homing and Traffic Engineering are both, in some sense, uses of Multi-homing and Traffic Engineering are both, in some sense, uses of
LISP for routing, but there are many other routing-related uses for LISP for routing, but there are many other routing-related uses for
LISP. LISP.
One of the major original motivations for the separation of location One of the major original motivations for the separation of location
and identity in general, and thus LISP, was to reduce the growth of and identity in general, and thus LISP, was to reduce the growth of
the routing tables in the so-called 'Default-Free-Zone' (DFZ) - the the routing tables in the so-called 'Default-Free-Zone' (DFZ) - the
core of the Internet, the part where routes to _all_ ultimate core of the Internet, the part where routes to _all_ ultimate
destinations must be available. LISP is expected to help with this; destinations must be available. LISP is expected to help with this;
for more detail, see Section 11.6, below. for more detail, see Section 12.4, "LISP and DFZ Routing", below.
LISP may also have more local applications in which it can help with LISP may also have more local applications in which it can help with
routing; see, for instance, [CorasBGP]. routing; see, for instance, [CorasBGP].
5.5. Mobility 5.5. Mobility
Mobility is yet another place where separation of location and Mobility is yet another place where separation of location and
identity is obviously a key part of a clean, efficient and high- identity is obviously a key part of a clean, efficient and high-
functionality solution. Considerable experimentation has been functionality solution. Considerable experimentation has been
completed on doing mobility with LISP. completed on doing mobility with LISP.
The mobility provided by LISP allows active sessions to survive moves
(provided of course that there is not a period of inaccessability
which exceeds a timeout). LISP mobility also will typically have
better packet 'stretch' (i.e. increase in path length) compared to
traditional mobility schemes, which use a 'home agent'.
5.6. IP Version Reciprocal Traversal 5.6. IP Version Reciprocal Traversal
Note that LISP 'automagically' allows intermixing of various IP Note that LISP inherently supports intermixing of various IP versions
versions for packet carriage; IPv4 packets might well be carried in for packet carriage; IPv4 packets might well be carried in IPv6, or
IPv6, or vice versa, depending on the network's configuration. This vice versa, depending on the network's configuration.
would allow an 'island' of operation of one type to be
This capability allows an 'island' of operation of one type to be
'automatically' tunneled over a stretch of infrastucture which only 'automatically' tunneled over a stretch of infrastucture which only
supports the other type. supports the other type.
While the machinery of LISP may seem too heavyweight to be good for While the machinery of LISP may seem too heavy-weight to be good for
such a mundane use, this is not intended as a 'sole use' case for such a mundane use, this is not intended as a 'sole use' case for
deployment of LISP. Rather, it is something which, if LISP is being deployment of LISP. Rather, it is something which, if LISP is being
deployed anyway (for its other advantages), is an added benefit that deployed anyway (for its other advantages), is an added benefit that
one gets 'for free'. one gets 'for free'.
5.7. Local Uses 5.7. Local Uses
LISP has a number of use cases which are within purely local LISP has a number of use cases which are within purely local
contexts, i.e. not in the larger Internet. These fall into two contexts, i.e. not in the larger Internet. These fall into two
categories: uses seen on the Internet (above), but here on a private categories: uses seen on the Internet (above), but here on a private
skipping to change at line 665 skipping to change at page 16, line 24
Among the former are multi-homing, IP version traversal, and support Among the former are multi-homing, IP version traversal, and support
of VPN's for segmentation and multi-tenancy (i.e. a spatially of VPN's for segmentation and multi-tenancy (i.e. a spatially
separated private VPN whose components are joined together using the separated private VPN whose components are joined together using the
public Internet as a backbone). public Internet as a backbone).
Among the latter class, non-Internet applications which have no Among the latter class, non-Internet applications which have no
analog on the Internet, are the following example applications: analog on the Internet, are the following example applications:
virtual machine mobility in data centers; other non-IP EID types such virtual machine mobility in data centers; other non-IP EID types such
as local network MAC addresses, or application specific data. as local network MAC addresses, or application specific data.
Several of the applications listed in this section are the ones which
have been most popular for LISP in practise; these include virtual
networks, and virtual machine mobility.
These often show a synergistic tendency, in that a site which
installs LISP to do one, often finds that then becomes a small matter
to use it for the second. Given all the things which LISP can do, it
is hoped that this synergistic effect will continue to expand LISP's
uses.
6. Major Functional Subsystems 6. Major Functional Subsystems
LISP has only two major functional sub-systems - the collection of LISP has only two major functional sub-systems - the collection of
LISP packet switches (the xTRs), and the mapping system, which LISP packet switches (the xTRs), which form the 'data plane' of LISP;
manages the mapping database. The purpose and operation of each is and the mapping system, the most important part of the 'control
described at a high level below, and then, later on, in a fair amount plane', which manages the mapping database.
of detail, in separate sections on each (Sections Section 9 and
Section 10, respectively). The purpose and operation of each is described at a high level below,
and then, later on, in a fair amount of detail, in separate sections
on each (Sections Section 9, "Data Plane - xTRs", and Section 10,
"Control Plane - The Mapping System", respectively).
6.1. xTRs 6.1. xTRs
xTRs are fairly normal packet switches, enhanced with a little extra xTRs are IPvN packet switches which have been augmented with extra
functionality in both the data and control planes, to perform LISP functionality in both the data and control planes, to perform LISP
data and control functionality. data and control functionality (respectively).
The data plane functions in ITRs include deciding which packets need The data plane functions in ITRs include deciding which packets need
to be given LISP processing (since packets to non-LISP hosts may be to be given LISP processing (since packets to non-LISP hosts may be
sent 'vanilla'); i.e. looking up the mapping; encapsulating the sent as they are); i.e. looking up the mapping; encapsulating
packet; and sending it to the ETR. This encapsulation is done using (wrapping) the packet; and sending it to the ETR. To the extent that
UDP [RFC768] (for reasons to be explained below, in Section 9.2), traffic engineering features are in use for a particular EID, the
along with an additional IPvN header (to hold the source and ITRs implement them as well.
destination RLOCs). To the extent that traffic engineering features
are in use for a particular EID, the ITRs implement them as well.
In the ETR, the data plane simply unwraps the packets, and forwards This encapsulation is done using UDP [RFC768] (for reasons to be
the now-normal packets to the ultimate destination. explained below, in Section 9.2, "UDP Encapsulation Details"), along
with an additional outer IPvN header (to hold the source and
destination RLOCs).
In the ETR, the data plane simply decapsulates (unwraps) the packets,
and forwards the now-normal packets to the ultimate destination.
Control plane functions in ITRs include: asking for {EID->RLOC} Control plane functions in ITRs include: asking for {EID->RLOC}
mappings via Map-Request control messages; handling the returning mappings via request control messages (Map-Request packets); handling
Map-Replies which contain the requested information; managing the the returning reply control messages (Map-Reply packets), which
local cache of mappings; checking for the reachability and liveness contain the requested information; managing the local cache of
of their neighbour ETRs; and checking for outdated mappings and mappings; checking for the reachability and liveness of their
requesting updates. neighbour ETRs; and checking for outdated mappings and requesting
updates.
In the ETR, control plane functions include participating in the In the ETR, control plane functions include participating in the
neighbour reachability and liveness function (see Section 12.4); neighbour reachability and liveness function (see Section 13.4,
interacting with the mapping sub-system (next section); and answering "Neighbour ETR Liveness"); interacting with the mapping sub-system to
requests for mappings (ditto). let it know what mapping this ETR can provide (see Section 6.2.2,
"Interface to the Mapping System"); and answering requests from ITRs
for those mappings (ditto).
6.1.1. Mapping Cache Performance 6.1.1. Mapping Cache Performance
As mentioned, studies have been performed to verify that caching As mentioned, studies have been performed to verify that caching
mappings in ITRs is viable, in practical engineering terms. These mappings in ITRs is viable, in practical engineering terms. These
studies not only verified that such caching is feasible, but also studies not only verified that such caching is feasible, but also
provided some insight for designing ITR mapping caches. provided some insight for designing ITR mapping caches.
Obviously, these studies are all snapshots of a particular point in Obviously, these studies are all snapshots of a particular point in
time, and as the Internet continues its life-cycle they will time, and as the Internet continues its life-cycle they will
increasingly become out-dated. However, they are useful because they increasingly become out-dated. However, they are useful because they
provide an insight into how well LISP can be expected to perform, and provide an insight into how well LISP can be expected to perform, and
scale, over time. scale, over time.
The first, [Iannone], was performed in the very early stages of the Full details of the results are too lengthy to include here; see
LISP effort, to verify that that approach was feasible. First, [Perspective], Section "Mapping Cache Performance" for more.
packet traces of all traffic over the external connection of a large
university (around 10,000 users) over a week-long period were Briefly, however, the first, [Iannone], was performed in the very
collected. Simulations driven by these recording were then early stages of the LISP effort, to verify that that caching approach
performed; a variety of control settings on the cache were used, to was feasible.
study the effects of varying the settings. The simulations set no
limit on the total cache size, but used a range of cache retention Packet traces of all traffic over the external connection of a large
times (i.e. an entry that remained unused longer than a fixed university over a week-long period were collected; simulations driven
retention time was discarded), from 3 minutes, up to 300 minutes. by these recording were then performed. A variety of control
settings on the cache were used, to study the effects of varying the
settings.
First, the simulation gave the cache sizes that would result from First, the simulation gave the cache sizes that would result from
such a cache design. It showed that the resulting cache sizes ranged such a cache design: it showed that the resulting cache sizes ranged
from 7,500 entries (at night, with the shortest retention time) up to from 7,500 entries, up to about 100,000 (depending on factors such as
about 100,000. Using some estimations as to i) how many RLOCs the traffic and entry retention time). Using some estimations as to how
average mapping would have (since this will affect its size), and ii) much memory mapping entries would use, this indicated cache sizes of
how much memory it would take to store a mapping, this indicated between roughly 100 Kbytes and a few Mbytes.
cache sizes of between roughly 100 Kbytes and a few Mbytes.
Of more interest, in a way, were the results regarding two important Of more interest, in a way, were the results regarding two important
measurements of the effectiveness of the cache: i) the hit ratio measurements of the effectiveness of the cache: i) the hit ratio
(i.e. the share of references which could be satisified by the (i.e. the share of references which could be satisified by the
cache), and ii) the miss _rate_ (since control traffic overhead is cache), and ii) the miss _rate_ (since control traffic overhead is
one of the chief concerns when using a cache). These results were one of the chief concerns when using a cache). These results were
also encouraging: miss (and hence lookup) rates ranged (again, also encouraging: miss (and hence lookup) rates ranged from 30 per
depending on the time of day, cache settings, etc) from 30 per minute, up to 3,000 per minute.
minute, up to 3,000 per minute (i.e. 150 per second; with the
shortest timeout, and thus the smallest cache). Significantly, this Significantly, this was substantially lower than the amount of
was substantially lower than the amount of observed DNS traffic, observed DNS traffic, which ranged from 1,800 packets per minute up
which ranged from 1,800 packets per minute up to 15,000 per minute. to 15,000 per minute. The results overall showed that using a
demand-loaded cache was an entirely plausible design approach: both
cache size, and the control plane traffic load, were definitely
feasible.
The second, [Kim], was in general terms similar, except that it used The second, [Kim], was in general terms similar, except that it used
data from a large ISP (taken over two days, at different times of the data from a large ISP, one with about three times as many users as
year), one with about three times as many users as the previous the previous study. It used the same cache design philosophy (the
study. It used the same cache design philosophy (the cache size was cache size was not fixed), but slightly different, lower, retention
not fixed), but slightly different, lower, retention time values: 60 time values.
seconds, 180 seconds, and 1,800 seconds (30 minutes), since the
previous study had indicated that extremely long times (hours) had
little additional benefit.
The results were similar: cache sizes ranges from 20,000 entries with The results were similar: cache sizes ranges from 20,000 entries to
the shortest timeout, to roughly 60,000 with the longest; the miss roughly 60,000; the miss rate ranged from very roughly 400 per minute
rate ranged from very roughly 400 per minute (with the longest to very roughly 7,000 per minute, similar to the previous results.
timeout) to very roughly 7,000 per minute (with the shortest),
similar to the previous results.
Finally, a third study, [CorasCache], examined the effect of using a Finally, a third study, [CorasCache], examined the effect of using a
fixed size cache, and a purely Least Recently Used (LRU) cache fixed size cache, and a purely Least Recently Used (LRU) cache
eviction algorithm (i.e. no timeouts). It also tried to verify that eviction algorithm (i.e. no timeouts). It also tried to verify that
models of the performance of such a cache (using previous theoretical models of the performance of such a cache (using previous theoretical
work on caches) produced results that conformed with actual empirical work on caches) produced results that conformed with actual empirical
measurements. measurements.
It used yet another set of packet traces (some from an earlier study, It used yet another set of packet traces; using a cache size of
[Jakab]). Using a cache size of around 50,000 entries produced a around 50,000 entries produced a miss rate of around 1x10-4; again,
miss rate of around 1x10-4; again, definitely viable, and in line definitely viable, and in line with the results of the other studies.
with the results of the other studies.
6.2. Mapping System 6.2. The Mapping System
The mapping database is a distributed, and potentially replicated, The mapping system's entire purpose is to give ITRs on-demand access
database which holds mappings between EIDs (identity) and RLOCs to the mapping database, which is a distributed, and potentially
(location). To be exact, it contains mappings between EID blocks and replicated, database which holds mappings between EIDs (identity) and
RLOCs (the block size is given explicitly, as part of the syntax). RLOCs (location), along with needed ancillary data (e.g. lifetimes).
Support for blocks is both for minimizing the administrative To be exact, it contains mappings between EID blocks and RLOCs (the
configuration overhead, as well as for operational efficiency; e.g. block size is given explicitly, as part of the syntax). Support for
when a group of EIDs are behind a single xTR. blocks is both for minimizing the administrative configuration
overhead, as well as for operational efficiency; e.g. when a group of
EIDs are behind a single xTR.
However, the block may be (and often is) as small as a single EID. However, the block may be, and often is, as small as a single EID.
Since mappings are only loaded upon demand, if smaller blocks become However, since mappings are only loaded upon demand, if smaller
predominant, then the increased size of the overall database is far blocks become predominant, then the increased size of the overall
less problematic than if the routing table came to be dominated by database is far less problematic than if the Internet's routing
such small entries. tables came to be dominated by such small entries.
A particular node may have more than one RLOC, or may change its A particular EID (or EID block) may have more than one RLOC, or may
RLOC(s), while keeping its singlar identity. change its RLOC(s), while keeping its basic identity.
The mapping contains not just the RLOC(s), but also (for each RLOC Also, in general, throughout LISP, anyplace a name (EID, RLOC, etc)
for any given EID) priority and weight (to allow allocation of load appears in a control packet, the packet format also includes an
between several RLOCs at a given priority); this allows a certain Address Family Identifier (AFI) for that name. [AFI] The inclusion
amount of traffic engineering to be accomplished with LISP. of the AFI allows LISP (and in particular, the mapping system
interface, as embodied in those control packets) a great deal of
flexibility. (See [Perspective], Section "Namespaces" for more on
this.)
RLOC(s) may be compound names; see [Improvements], Section "LISP
Canonical Address Format (LCAF)" for more.
Finally, the mapping from an EID (or EID block) contains not just the
RLOC(s), but also (for each RLOC for any given EID entry) priority
and weight fields (to allow allocation of load between several RLOCs
at a given priority); this allows a certain amount of traffic
engineering to be accomplished with LISP.
6.2.1. Mapping System Organization 6.2.1. Mapping System Organization
The mapping system is actually split into what are effectively three The mapping system is actually split into what are effectively three
major functional sub-systems (although the latter two are closely major functional sub-systems (although the latter two are closely
integrated, and appear to most entities in the LISP system as a integrated, and appear to most entities in the LISP system as a
single sub-system). single sub-system).
The first covers the actual mappings themselves; they are held by the The first covers the actual mappings themselves; they are held by the
ETRs, and an ITR which needs a mapping gets it (effectively) directly ETRs, and an ITR which needs a mapping gets it (effectively) directly
from the ETR. This co-location of the authoritative version of the from the ETR. This co-location of the authoritative version of the
mappings, and the forwarding functionality which it describes, is an mappings, and the forwarding functionality which it describes, is an
instance of fate-sharing. [Clark] instance of fate-sharing. [Clark]
To find the appropriate ETR(s) to query for the mapping, the second To find the appropriate ETR(s) to query for the mapping, the second
two sub-systems form an 'indexing system', itself also a distributed, two sub-systems form an 'indexing system', itself also a distributed,
potentally replicated database. It provides information on which potentially replicated database. It provides information on which
ETR(s) are authoritative sources for the various {EID -> RLOC} ETR(s) are authoritative sources for the various {EID -> RLOC}
mappings which are available. The two sub-systems which form it are mappings which are available. The two sub-systems which form it are
the user interface sub-system, and indexing sub-system (which holds the client interface sub-system, and indexing sub-system (which holds
and provides the actual information). and provides the actual information).
6.2.2. Interface to the Mapping System 6.2.2. Interface to the Mapping System
The client interface to the indexing system from an ITR's point of The client interface to the indexing system from an ITR's point of
view is not with the indexing sub-system directly; rather, it is view is not with the indexing sub-system directly; rather, it is
through the client-interface sub-system, which is provied by devices through the client-interface sub-system, which is provied by devices
called Map Resolvers (MRs). called Map-Resolvers (MRs).
ITRs send request control messages (Map-Request packets) to an MR. ITRs send request control messages (Map-Request packets) to an MR.
(This interface is probably the most important standardized interface (This interface is probably the most important standardized interface
in LISP - it is the key to the entire system.) in LISP - it is the key to the entire system.) The MR then uses the
indexing sub-system to allow it to forward the Map-Request to an
appropriate MS, which in turn sends the Map-Request on to the
appropriate ETR. The latter is authoritative for the actual contents
of all mappings for those EID namespace blocks which have been
delegated to it.
The MR then uses the indexing sub-system to allow it to forward the The ETR then formulates reply control messages (Map-Reply packets),
Map-Request to the appropriate ETR. The ETR formulates reply control which are sent to the ITR. The details of the indexing sub-system
messages (Map-Reply packets), which are sent to the ITR. The details are thus hidden from the ITRs.
of the indexing system are thus hidden from the ITRs.
(Note that in some cases, it is desirable for the MS to reply on
behalf of the ETR, in so-called 'proxy' mode. This behaviour can be
selected when the ETR registers with the MR, described immediately
below.)
Similarly, the client interface to the indexing system from an ETR's Similarly, the client interface to the indexing system from an ETR's
point of view is through devices called Map Servers (MSs - admittedly point of view is through devices called Map-Servers (MSs - perhaps a
a poorly chosen term, since their primary function is not to respond poorly chosen term, since their primary function is not to send
to queries, but it's too late to change it now). responses to queries from clients of the mapping system).
ETRs send registration control messages (Map-Register packets) to an ETRs send registration control messages (Map-Register packets) to an
MS, which makes the information about the mappings which the ETR MS, which makes the information about the mappings which the ETR
indicates it is authoritative for available to the indexing system. indicates it is authoritative for available to the indexing sub-
system.
The MS formulates a reply control message (the Map-Notify packet), The MS formulates a reply control message (the Map-Notify packet),
which confirms the registration, and is returned to the ETR. The which confirms the registration, and is returned to the ETR. The
details of the indexing system are thus likewise hidden from the details of the indexing sub-system are thus likewise hidden from the
'ordinary' ETRs. 'ordinary' ETRs.
The fact that the details of the indexing sub-system are entirely
hidden from xTRs gives considerably flexibility to this aspect of
LISP. As long as any potential indexing sub-system can track where
mappings are, it could potentially be used; this would allow the
actual indexing sub-system to be replaced without needing to modify
the clients - as has happened once already (see below).
6.2.3. Indexing Sub-system 6.2.3. Indexing Sub-system
The current indexing sub-system is the Delegated Database Tree (DDT), The current indexing sub-system is the Delegated Database Tree (DDT),
which is very similar to DNS. [DDT], [RFC1034] However, unlike DNS, which is very similar to DNS ([DDT], [RFC1034]), although unlike DNS,
the actual mappings are not handled by DDT; DDT (as part of the DDT was designed from the start to be secured. Also unlike DNS, the
indexing system) merely identifies the ETRs which hold the actual actual mappings are not handled by DDT; DDT, as the indexing sub-
mappings. system, merely identifies the ETRs which hold the actual mappings.
DDT replaced an earlier indexing sub-system, ALT ([Perspective], DDT replaced an earlier indexing sub-system, ALT (Appendix B.4, "The
section "Appendices-ALT"); this swap validated the concept of having ALT Mapping Indexing Sub-system"); this swap validated the concept of
a separate client-interface sub-system, which would allow the actual having a client-interface sub-system between the indexing sub-system,
indexing sub-system to be replaced without needing to modify the and the clients.
clients.
6.2.3.1. DDT Overview 6.2.3.1. DDT Overview
Conceptually, DDT is fairly simple: like DNS, in DDT the delegation Conceptually, DDT is fairly simple: like DNS, in DDT the delegation
of the EID namespace ([Perspective], Section "Namespaces-XEIDs") is of the EID namespace ([Perspective], Section "Namespaces-XEIDs") is
instantiated as a tree of DDT 'nodes', starting with the 'root' DDT instantiated as a tree of DDT 'nodes', starting with the 'root' DDT
node. Each node is responsible (authoritative?) for one or more node. Each node is responsible (authoritative?) for one or more
blocks of the EID namespace. blocks of the EID namespace.
The 'root' node is reponsible for the entire namespace; any DDT node The 'root' node is reponsible for the entire namespace; any DDT node
can 'delegate' part(s) of its block(s) of the namespace to child DDT can 'delegate' part(s) of its block(s) of the namespace to child DDT
node(s). The child node(s) can in turn further delgate (necessarily node(s). The child node(s) can in turn further delegate (necessarily
smaller) blocks of namespace to their children, through as many smaller) blocks of namespace to their children, through as many
levels as are needed (for operational, administrative, etc, needs). levels as are needed (for operational, administrative, etc, needs).
Just as with DNS, for reasons of performance, reliability and Just as with DNS, for reasons of performance, reliability and
robustness, any particular node in the DDT delegation tree may be robustness, any particular node in the DDT delegation tree may be
instantiated in more than one redundant physical server machines. instantiated in more than one redundant physical server machines.
Obviously, all the servers which instantiate a particular node in the Obviously, all the servers which instantiate a particular node in the
tree have to have identical data about that node. tree have to have identical data about that node; if they do not,
when a Map-Request is sent to one that does not have consistent
information with its other sibling(s), incorrect results will be
returned.
Also, although the delegation hierarchy is a strict tree {{check - do Also, although the delegation hierarchy is a strict tree , a single
all servers for the delegation of block X have to return the same DDT server could be responsible (authoritative?) for more than one
list of servers for that block?}}, a single DDT server could be block of the EID namespace.
responsible (authoritative?) for more than one block of the EID
namespace.
Eventually, leaf nodes in the DDT tree assign ({{delegate? - it's all Eventually, leaf nodes in the DDT tree statically delegate EID
static configured, nothing is dynamic}}) EID namespace blocks to namespace blocks to MS's, which are DDT terminal nodes; i.e. a leaf
MS's, which are DDT terminal nodes; i.e. a leaf of the tree is of the tree is reached when the delegation points to an MS instead of
reached when the delegation points to an MS instead of to another DDT to another DDT node.
node.
The MS is in direct communication with the ETR(s) which both i) are The MS is in direct communication with the ETR(s) which both i) are
authoritative for the mappings for that block, and ii) handle traffic authoritative for the mappings for that block, and ii) handle traffic
to that block of EID namespace. to that block of EID namespace.
6.2.3.2. Use of DDT by MRs 6.2.3.2. Use of DDT by MRs
An MR which wants to find a mapping for a particular EID first An MR which wants to find a mapping for a particular EID first
interacts with the nodes of the DDT tree, discovering (by querying interacts with the nodes of the DDT tree, discovering (by querying
DDT nodes) the chain of delegations which cover that EID. Eventually DDT nodes) the chain of delegations which cover that EID. Eventually
skipping to change at line 928 skipping to change at page 22, line 44
some locally cached delegation information, perhaps loading some some locally cached delegation information, perhaps loading some
missing delegation entries into their delegation cache, and finally missing delegation entries into their delegation cache, and finally
sending the Map-Request to the appropriate MS. sending the Map-Request to the appropriate MS.
The big advantage of DDT over the ALT, in performance terms, is that The big advantage of DDT over the ALT, in performance terms, is that
it allows MRs to interact _directly_ with distant DDT nodes (as it allows MRs to interact _directly_ with distant DDT nodes (as
opposed to the ALT, which _always_ required mediation through opposed to the ALT, which _always_ required mediation through
intermediate nodes); caching of information about those distant nodes intermediate nodes); caching of information about those distant nodes
allows DDT to make extremely effective use of this capability. allows DDT to make extremely effective use of this capability.
It should also be noted that the delegation tree is fairly static,
since it reflects namespace allocations, which are themselves fairly
static. This stability has several important consequences. First,
it increases the performance of the mapping system, since
intermediate nodes almost never need to be re-queried. Second, it is
not necessary to include a mechanism to find outdated delegations.
The _mappings_, however, may change at a high rate, and the system is
designed to make sure that such changes are acted upon. This allows
LISP to provide a number of capabilities, such as mobility.
7. Examples of Operation 7. Examples of Operation
To aid in comprehension, a few examples are given of user packets To aid in comprehension, a few examples are given of user packets
traversing the LISP system. The first shows the processing of a traversing the LISP system. The first shows the processing of a
typical user packet, i.e. what the vast majority of user packets will typical user packet, i.e. what the vast majority of user packets will
see. The second shows what happens when the first packet to a see. The second shows what happens when the first packet to a
previously-unseen ultimate destination (at a particular ITR) is to be previously-unseen ultimate destination (at a particular ITR) is to be
processed by LISP. processed by LISP.
7.1. An Ordinary Packet's Processing 7.1. An Ordinary Packet's Processing
This case follows the processing of a typical user packet (for This case follows the processing of a typical user packet (for
instance, a normal TCP data or acknowledgment packet associated with instance, a normal TCP data or acknowledgment packet associated with
an already-open TCP connection) as it makes its way from the original an already-open TCP connection) - i.e. not the first packet sent from
source host to the ultimate destination. a given source to a given destination - as it makes its way from the
original source host to the ultimate destination.
When the packet has made its way through the local site to an ITR When the packet has made its way through the local site to an ITR
(which is also a border router for the site), the border router looks (which in this case is a border router for the site), the border
up the desination address (an EID) in its local mapping cache. It router looks up the destination address (an EID) in its local mapping
finds a mapping, which instructs it to wrap the packet in an outer cache. For EIDs which are IPvN addresses, this lookup uses the usual
IPvN 'longest prefix match' algorithm.
It finds a mapping, which instructs it to wrap the packet in an outer
header (an IP packet, containing a UDP packet which contains a LISP header (an IP packet, containing a UDP packet which contains a LISP
header, and then the user's original packet). The destination header, and then the user's original packet (see Section 9.2, "UDP
address in the outer header is set by the ITR to the RLOC of the Encapsulation Details", for the reasons for this particular choice).
destination ETR. The destination address in the outer header is set by the ITR to the
RLOC of the destination ETR.
The packet is then sent off through the Internet, using normal The packet is then sent off through the Internet, using normal
Internet routing tables, etc. Internet routing tables, etc.
On arrival at the destination ETR, the ETR will notice that it is On arrival at the destination ETR, the ETR will notice that it is
listed as the destination in the outer header. It will examine the listed as the destination in the outer header. It will examine the
packet, detect that it is a LISP packet, and unwrap it. It will then packet, detect that it is a LISP packet, and unwrap it. It will then
examine the header of the user's original packet, and forward it examine the header of the user's original packet, and forward it
internally, through the local site, to the ultimate destination. internally, through the local site, to the ultimate destination.
At the ultimate destination, the packet will be processed, and may At the ultimate destination, the packet will be processed, and may
produce a return packet, which follows the exact same process in produce a return packet, which follows the exact same process in
reverse - with the exception that the roles of the ITR and ETR are reverse - with the exception that the roles of the ITR and ETR are
swapped. swapped.
7.2. A Mapping Cache Miss 7.2. A Mapping Cache Miss
If a host sends a packet, and it gets to the ITR, and the ITR both i) If a host sends a packet, and it gets to the ITR, and the ITR both i)
determines that it needs to perform LISP processing on the user data determines that it needs to perform LISP processing on the user data
packet, but ii) does not yet have a mapping cache entry which covers packet, but ii) does not yet have a mapping cache entry which covers
that destination EID, then more complex processing ensues. that destination EID, then additional processing ensues; it has to
look up the mapping in the mapping system (as previously described in
Section 4.2, "Basic Functionality").
It sends a Map-Request packet, giving the destination EID it needs a The overall processing is shown below, in Figure 2:
mapping for, to its MR. The MR will look in its cache of delegation
information to see if it has the RLOC for the ETR for that
destination EID. If not, it will query the DDT system to find the
RLOC of the ETR. When it has the RLOC, it will send the Map-Request
on to the ETR.
The ETR sends a Map-Reply to the ITR which needs the mapping; from Mapping System
then on, processing of user packets through that ITR to that ultimate
destination proceeds as above. (Typically, like many ARP ----- -----
implementations, the original user packet will have been discarded, | | 4 | |
not cached waiting for the mapping to be found. When the host Map Resolver | | -------> | | Map Server
retransmits the packet, the mapping will be there, and the packet | | | |
will be forwarded.) ----- -----
^ |
Key: | |
| |
-- = Control | |
== = Data | |
2 | 6 | 5
| --- |
Host A | / \ | Host B
| |_ \ V
----- ----- \ ----- -----
| | 1 | | 7 | | 8 | |
| | =====> | ITR | =======> | ETR | =====> | |
| | | | | | | |
----- ----- ----- -----
Figure 2: Packet Flow With Missing Mapping
1. Source-EID sends packet (to Dest-EID) to ITR
2. ITR sends Map-Request to Map Resolver
3. (Not shown) Map-Resolver locates corrrect Map-Server for Dest-EID
4. Map-Resolver delivers Map-Request to Map-Server
5. Map-Server delivers Map-Request to ETR
6. ETR returns Map-Reply to ITR; ITR caches EID-to-RLOC(s) mapping
7. ITR uses mapping to encapsulate to ETR; sends user packet to ETR
8. ETR decapsulates packet, delivers to Dest-EID
The ITR first sends a Map-Request packet, giving the destination EID
it needs a mapping for, to its MR. The MR will look in its cache of
delegation information to find the node which is closest in the
delegation tree to that destination EID which it has information for.
If it does not have the RLOC of an appropriate MS, it will query the
DDT system, recursively if need be, in order to eventually find the
RLOC of such an MS.
When it has the MS's RLOC, it will send the Map-Request on to the MS,
which then sends it on to an appropriate ETR. The ETR sends a Map-
Reply to the ITR which needs the mapping; from then on, processing of
user packets through that ITR to that ultimate destination proceeds
as above.
Often (as with many ARP implementations), the original user packet
will have been discarded, and not queued waiting for the mapping to
be returned. When the host retransmits such a packet, the mapping
will be there, and the packet will be forwarded. Alternatively, it
might have been queued, or perhaps it was forwarded using a PITR.
(Section 4.4, "Interworking With Non-LISP-Capable Endpoints")>
8. Design Approach 8. Design Approach
Before describing LISP's components in more detail below, it it worth Before describing LISP's components in more detail below, it it worth
pointing out that what may seem, in some cases, like odd (or poor) pointing out that what may seem, in some cases, like odd (or poor)
design approaches do in fact result from the application of a design approaches do in fact result from the application of a
thought-through, and consistent, design philosophy used in creating thought-through, and consistent, design philosophy used in creating
them. them.
This design philosophy is covered in detail in in [Perspective], This design philosophy is covered in detail in in [Perspective],
Section "Design"), and readers who are interested in the 'why' of Section "Design"), and readers who are interested in the 'why' of
various mechanisms should consult that; reading it may make clearer various mechanisms should consult that; reading it may make clearer
the reasons for some engineering choices in the mechanisms given the reasons for some engineering choices in the mechanisms given
here. here.
9. xTRs 9. Data Plane - xTRs
As mentioned above (in Section 6.1), xTRs are the basic data-handling As mentioned above (in Section 6.1, "xTRs"), xTRs are the basic data-
devices in LISP. This section explores some advanced topics related handling devices in LISP, and, as such, form the LISP data plane.
to xTRs. This section explores some advanced topics related to xTRs.
Careful rules have been specified for both TTL and ECN [RFC3168] to Careful rules have been specified for both TTL and ECN [RFC3168] to
ensure that passage through xTRs does not interfere with the ensure that passage through xTRs does not interfere with the
operation of these mechanisms. In addition, care has been taken to operation of these mechanisms. In addition, care has been taken to
ensure that 'traceroute' works when xTRs are involved. ensure that 'traceroute' works when xTRs are involved.
9.1. When to Encapsulate 9.1. When to Encapsulate
An ITR knows that an ultimate destination is 'running' LISP (remember An ITR knows that an ultimate destination is 'running' LISP (remember
that the destination machine itself probably knows nothing about that the destination machine itself probably knows nothing about
LISP), and thus that it should perform LISP processing on a packet LISP), and thus that it should perform LISP processing on a packet
(including potential encapsulation) if it has an entry in its local (including potential encapsulation) if it has an entry in its local
mapping cache that covers the destination EID. mapping cache that covers the destination EID.
Conversely, if the cache contains a 'negative' entry (indicating that Conversely, if the cache contains a 'negative' entry (indicating that
the ITR has previously attempted to find a mapping that covers this the ITR has previously attempted to find a mapping that covers this
EID, and it has been informed by the mapping system that no such EID, and it has been informed by the mapping system that no such
mapping exists), it knows the ultimate destination is not running mapping exists), it knows the ultimate destination is not running
LISP, and the packet can be forwarded normally. LISP, and the packet can be forwarded natively (i.e. not LISP-
encapsulated).
Note that the ITR cannot simply depend on the appearance, or non- Note that the ITR cannot simply depend on the appearance, or non-
appearance, of the destination in the routing tables in the DFZ, as a appearance, of the destination in the routing tables in the DFZ, as a
way to tell if an ultimate destination is a LISP node or not, because way to tell if an ultimate destination is a LISP node or not. That
mechanisms to allow interoperation of LISP sites and 'legacy' sites is because mechanisms to allow interoperation of LISP sites and
necessarily involve advertising LISP sites' EIDs into the DFZ. 'legacy' sites necessarily involve advertising LISP sites' EIDs into
the DFZ; in other words, LISP sites which need to interoperate with
'legacy' nodes will appear in the DFZ routing tables, along with non-
LISP sites.
9.2. UDP Encapsulation Details 9.2. UDP Encapsulation Details
The UDP encapsulation used by LISP for carrying traffic from ITR to The UDP encapsulation used by LISP for carrying traffic from ITR to
ETR, and many of the details of how it works, were all chosen for ETR, and many of the details of how it works, were all chosen for
very practical reasons. very practical reasons.
Use of UDP (instead of, say, a LISP-specific protocol number) was Use of UDP (instead of, say, a LISP-specific protocol number) was
driven by the fact that many devices filter out 'unknown' protocols, driven by the fact that many devices filter out 'unknown' protocols,
so adopting a non-UDP encapsulation would have made the initial so adopting a non-UDP encapsulation would have made the initial
deployment of LISP harder - and our goal (see Section 3.1) was to deployment of LISP harder - and our goal (see Section 3.1,
make the deployment as easy as possible. "Economics") was to make the deployment as easy as possible.
The UDP source port in the encapsulated packet is a hash of the The UDP source port in the encapsulated packet is a 5-way hash of the
original source and ultimate destination; this is because many ISPs original source and ultimate destination in the inner header, along
use multiple parallel paths (so-called 'Equal Cost Multi-Path'), and with the ports, and the protocol.
load-share across them. Using such a hash in the source-port in the
outer header both allows LISP traffic to be load-shared, and also This is because many ISPs use multiple parallel paths (so-called
ensures that packets from individual connections are delivered in 'Equal Cost Multi-Path'), and load-share across them. Using such a
order (since most ISPs try to ensure that packets for a particular hash in the source-port in the outer header both allows LISP traffic
{source, source port, destination, destination port} tuple flow along to be load-shared, and also ensures that packets from individual
a single path, and do not become disordered).. connections are delivered in order (since most ISPs try to ensure
that packets for a particular {source, source port, destination,
destination port} tuple flow along a single path, and do not become
disordered).
The UDP checksum is zero because the inner packet usually already has The UDP checksum is zero because the inner packet usually already has
a end-end checksum, and the outer checksum adds no value. [Saltzer] a end-end checksum, and the outer checksum adds no value. [Saltzer]
In most exising hardware, computing such a checksum (and checking it In most exising hardware, computing such a checksum (and checking it
at the other end) would also present an intolerable load, for no at the other end) would also present an intolerable load, for no
benefit. benefit.
9.3. Header Control Channel 9.3. Header Control Channel
LISP provides a multiplexed channel in the encapsulation header. It LISP provides a multiplexed channel in the encapsulation header. It
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the contents and meaning of which vary, depending on which flags are the contents and meaning of which vary, depending on which flags are
set. This allows these fields to be 'multiplexed' among a number of set. This allows these fields to be 'multiplexed' among a number of
different low-duty-cycle functions, while minimizing the space different low-duty-cycle functions, while minimizing the space
overhead of the LISP encapsulation header. overhead of the LISP encapsulation header.
9.3.1. Mapping Versioning 9.3.1. Mapping Versioning
One important use of the multiplexed control channel is mapping One important use of the multiplexed control channel is mapping
versioning; i.e. the discovery of when the mapping cached in an ITR versioning; i.e. the discovery of when the mapping cached in an ITR
is outdated. To allow an ITR to discover this, identifying sequence is outdated. To allow an ITR to discover this, identifying sequence
numbers are applied to different versions of a mappping. numbers are applied to different versions of a mappping. [RFC6834]
[Versioning] This allows an ITR to easily discover when a cached This allows an ITR to easily discover when a cached mapping has been
mapping has been updated by a more recent variant. updated by a more recent variant.
Version numbers are available in control messages (Map-Replies), but Version numbers are available in control messages (Map-Replies), but
the initial concept is that to limit control message overhead, the the initial concept is that to limit control message overhead, the
versioning mechanism should primarily use the multiplex user data versioning mechanism should primarily use the multiplex user data
header control channel. header control channel.
Versioning can operate in both directions: an ITR can advise an ETR Versioning can operate in both directions: an ITR can advise an ETR
what version of a mapping it is currently using (so the ETR can what version of a mapping it is currently using (so the ETR can
notify it if there is a more recent version), and ETRs can let ITRs notify it if there is a more recent version), and ETRs can let ITRs
know what the current mapping version is (so the ITRs can request an know what the current mapping version is (so the ITRs can request an
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header; when that ETR (acting as an ITR) sends some other user data header; when that ETR (acting as an ITR) sends some other user data
packet back to the ITR (acting in turn as an ETR), that nonce is packet back to the ITR (acting in turn as an ETR), that nonce is
carried in the header of that packet, allowing the original ITR to carried in the header of that packet, allowing the original ITR to
confirm that its packets are reaching that ETR. confirm that its packets are reaching that ETR.
Note that lack of a response is not necessarily _proof_ that Note that lack of a response is not necessarily _proof_ that
something has gone wrong - but it stronly suggests that something something has gone wrong - but it stronly suggests that something
has, so other actions (e.g. a switch to an alternative ETR, if one is has, so other actions (e.g. a switch to an alternative ETR, if one is
listed; a direct probe; etc) are advised. listed; a direct probe; etc) are advised.
(See Section 12.5 for more about Echo Nonces.) (See Section 13.5, "Neighbour ETR Reachability", for more about Echo
Nonces.)
9.3.3. Instances 9.3.3. Instances
Another use of these header fields is for 'Instances' - basically, Another use of these header fields is for 'Instances' - basically,
support for VPN's across backbones. [RFC4026] Since there is only support for VPN's across backbones. [RFC4026] Since there is only
one destination UDP port used for carriage of user data packets, and one destination UDP port used for carriage of user data packets, and
the source port is used for multiplexing (above), there is no other the source port is used for multiplexing (above), there is no other
way to differentiate among different destination address namespaces way to differentiate among different destination address namespaces
(which are often overlapped in VPNs). (which are often overlapped in VPNs).
9.4. Probing 9.4. Probing
RLOC-Probing (see [LISP], Section 6.3.2. "RLOC-Probing Algorithm" RLOC-Probing (see [RFC6830], Section 6.3.2. "RLOC-Probing Algorithm"
for details) is a mechanism method that an ITR can use to determine for details) is a mechanism method that an ITR can use to determine
with certainty that an ETR is up and reachable from the ITR. As a with certainty that an ETR is up and reachable from the ITR. As a
side-benfit, it gives a rough RTT estimates. side-benfit, it gives a rough RTT estimates.
It is quite a simple mechanism - an ITR simply sends a specially It is quite a simple mechanism - an ITR simply sends a specially
marked Map-Request directly to the ETR it wishes information about; marked Map-Request directly to the ETR it wishes information about;
that ETR sends back a specially marked Map-Reply. A Map-Request and that ETR sends back a specially marked Map-Reply. A Map-Request and
Map-Reply are used, rather than a special probing control-message Map-Reply are used, rather than a special probing control-message
pair, because as a side-benefit the ITR can discover if the mapping pair, because as a side-benefit the ITR can discover if the mapping
has been updated since it cached it. has been updated since it cached it.
The probing mechanism is rather heavy-weight and expensive (compared The probing mechanism is rather heavy-weight and expensive (compared
to mechanisms like the Echo-Nonce), since it costs a control message to mechanisms like the Echo-Nonce), since it costs a control message
from each side, so it should only be used sparingly. However, it has from each side, so it should only be used sparingly. However, it has
the advantages of providing information quickly (a single RTT), and the advantages of providing information quickly (a single RTT), and
being a simple, direct robust way of doing so. being a simple, direct robust way of doing so.
If the number of neighbour ETRs of the ITR is large, use of RLOC-
Probing to check on their reachability will result in considerable
control traffic; such control traffic has to be spread out to prevent
a load peak.
Obviously, if RLOC-Probing is the only mechanism being used to detect
unreachable neighbour ETRs, the rate at which RLOC-Probing is done
will control the timeliness of the detection of loss of reachability.
There is thus a tradeoff between overhead and responsiveness,
particular when an ITR has a large fanout of neighbour ETRs.
A further observation is that unless what are likely unreasonable
amounts of RLOC Probing are being done, Echo Nonce will generally
provide faster notification of loss of reachability (unless there is
little or no bi-directional traffic between the ITR and ETR).
9.5. Mapping Lifetimes and Timeouts 9.5. Mapping Lifetimes and Timeouts
Mappings come with a Time-To-Live, which indicate how long the Mappings come with a Time-To-Live, which indicate how long the
creator of the mapping expects them to be useful for. The TTL may creator of the mapping expects them to be useful for. The TTL may
also indicate that the mapping should not be cached at all, or it can also indicate that the mapping should not be cached at all, or it can
indicate that it has no particular lifetime, and the recipient can indicate that it has no particular lifetime, and the recipient can
chose how long to store it. chose how long to store it.
Mappings might also be discarded before the TTL expires, depending on Mappings might also be discarded before the TTL expires, depending on
what strategies the ITR is using to maintain its cache; if the what strategies the ITR is using to maintain its cache; if the
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9.6. Security of Mapping Lookups 9.6. Security of Mapping Lookups
LISP provides an optional mechanism to secure the obtaining of LISP provides an optional mechanism to secure the obtaining of
mappings by an ITR. [LISP-SEC] It provides protection against mappings by an ITR. [LISP-SEC] It provides protection against
attackers generating spurious Map-Reply messages (including replaying attackers generating spurious Map-Reply messages (including replaying
old Map-Replies), and also against 'over-claiming' attacks (where a old Map-Replies), and also against 'over-claiming' attacks (where a
malicious ETR by claims EID-prefixes which are larger what what have malicious ETR by claims EID-prefixes which are larger what what have
been actually delegated to it). been actually delegated to it).
Very briefly, the ITR provided a One-Time Key with its query; this Very briefly, the ITR provided a One-Time Key with its Map-Request;
key is used by both the MS (to verify the EID block that it has this key is used by both the MS (to sign an affirmation that it has
delegated to the ETR), and indirectly by the ETR (to verify the delegated that EID block to that ETR), and indirectly by the ETR (to
mapping that it is returning to the ITR). sign the mapping that it is returning to the ITR).
The specification for LISP-SEC suggests that the ITR-MR stage be The specification for LISP-SEC suggests that the ITR-MR stage be
cryptographically protected, and indicates that the existing cryptographically protected, and indicates that the existing
mechanisms for securing the ETR-MS stage are used to protect Map- mechanisms for securing the ETR-MS stage are used to protect Map-
Rquests also. It does assume that the channel from the MR to the MS Rquests also. It does assume that the channel from the MR to the MS
is secure (otherwise an attacker could obtain the OTK from the Map- is secure (otherwise an attacker could obtain the OTK from the Map-
Request and use it to forge a reply). Request and use it to forge a reply).
9.7. Mapping Gleaning in ETRs 9.7. Mapping Gleaning in ETRs
As an optimization to the mapping acquisition process, ETRs are As an optimization to the mapping acquisition process, ETRs are
allowed to 'glean' mappings from incoming user data packets, and also allowed to 'glean' mappings from incoming user data packets, and also
from incoming Map-Request control messages. {{Is this still there? from incoming Map-Request control messages. This is not secure, and
Check the latest version of the spec.}} This is not secure, and so so any such mapping must be 'verified' by sending a Map-Request to
any such mapping must be 'verified' by sending a Map-Request to get get an authoritative mapping. (See further discussion of the
an authoritative mapping. (See further discussion of the security security implications of this in [Perspective], Section "Security-
implications of this in [Perspective], Section "Security-xTRs".) xTRs".)
The value of gleaning is that most communications are two-way, and so The value of gleaning is that most communications are two-way, and so
if host A is sending packets to host B (therefore needing B's if host A is sending packets to host B (therefore needing B's
EID->RLOC mapping), very likely B will soon be sending packets back EID->RLOC mapping), very likely B will soon be sending packets back
to A (and thus needing A's EID->RLOC mapping). Without gleaning, to A (and thus needing A's EID->RLOC mapping). Without gleaning,
this would sometimes result in a delay, and the dropping of the first this would sometimes result in a delay, and the dropping of the first
return packet; this is felt to be very undesirable. return packet; this is felt to be very undesirable.
9.8. Fragmentation 9.8. Fragmentation
Several mechanisms have been proposed for dealing with packets which Several mechanisms have been proposed for dealing with packets which
are too large to transit the path from a particular ITR to a given are too large to transit the path from a particular ITR to a given
ETR. ETR.
One, called the 'stateful' approach, keeps a per-ETR record of the In one, called the 'stateful' approach, the ITR keeps a per-ETR
maximum size allowed, and sends an ICMP Too Big message to the record of the maximum size allowed, and sends an ICMP Too Big message
original source host when a packet which is too large is seen. to the original source host when a packet which is too large is seen.
In the other, referred to as the 'stateless' approach, for IPv4 In the other, referred to as the 'stateless' approach, for IPv4
packets without the 'DF' bit set, too-large packets are fragmented, packets without the 'DF' bit set, too-large packets are fragmented,
and then the fragments are forwarded; all other packets are and then the fragments are forwarded; all other packets are
discarded, and an ICMP Too Big message returned. discarded, and an ICMP Too Big message returned.
It is not clear at this point which approach is preferable. It is not clear at this point which approach is preferable.
10. The Mapping System 10. Control Plane - The Mapping System
As discussed already in Section 6.2, " The Mapping System", the LISP
mapping system is the most important part of LISP's control plane: it
i) maintains the database of mappings between EIDs, and the RLOCs at
which they are to be found, and ii) provides those mappings to ITRs
which request them, so that the ITRs can send traffic for a given EID
to the correct RLOC(s) for that EID.
RFC 1034 ("DNS Concepts and Facilities") has this to say about the RFC 1034 ("DNS Concepts and Facilities") has this to say about the
DNS name to IP address mapping system: DNS name to IP address database and mapping system:
"The sheer size of the database and frequency of updates suggest "The sheer size of the database and frequency of updates suggest
that it must be maintained in a distributed manner, with local that it must be maintained in a distributed manner, with local
caching to improve performance. Approaches that attempt to caching to improve performance. Approaches that attempt to
collect a consistent copy of the entire database will become more collect a consistent copy of the entire database will become more
and more expensive and difficult, and hence should be avoided." and more expensive and difficult, and hence should be avoided."
and this observation applies equally to the LISP mapping system. and this observation applies equally to the LISP mapping database and
mapping system.
To recap, the mapping system is split into an indexing sub-system, To briefly recap, the mapping system is split into three parts: i) an
which keeps track of where all the mappings are kept, and the indexing sub-system, which keeps track of where all the mappings are
kept; ii) the interface to the indexing system (which remains the
same, even if the actual indexing system is changed); and iii) the
mappings themselves, the authoritative copies of which are always mappings themselves, the authoritative copies of which are always
held by ETRs. held by ETRs.
10.1. The Mapping System Interface 10.1. The Mapping System Interface
As mentioned in Section 6.2.2, both of the inferfaces to the mapping As mentioned in Section 6.2.2, "Interface to the Mapping System",
system (from ITRs, and ETRs) are standardized, so that the more both of the inferfaces to the mapping system (from ITRs, and ETRs)
numerous xTRs do not have to be modified when the mapping indexing are standardized, so that the more numerous xTRs do not have to be
sub-system is changed. modified when the mapping indexing sub-system is changed.
(This precaution has already allowed the mapping system to be (This precaution has already allowed the mapping system to be
upgraded during LISP's evolution, when ALT was replaced by DDT.) upgraded during LISP's evolution, when ALT was replaced by DDT.)
This section describes the interfaces in a little more detail; for This section describes the interfaces in a little more detail; for
the details, see [MapInterface]. details, see [RFC6833].
10.1.1. Map-Request Messages 10.1.1. Map-Request Messages
The Map-Request message contains a number of fields, the two most The Map-Request message contains a number of fields, the two most
important of which are the requested EID block identifier (remember important of which are the requested EID block identifier (remember
that individual mappings may cover a block of EIDs, not just a single that individual mappings may cover a block of EIDs, not just a single
EID), and the Address Family Identifier (AFI) for that EID block. EID), and the Address Family Identifier (AFI) for that EID block.
[AFI] The inclusion of the AFI allows the mapping system interface
(as embodied in these control packets) a great deal of flexibility.
(See [Perspective], Section "Namespaces" for more on this.)
Other important fields are the source EID (and its AFI), and one or Other important fields are the source EID (and its AFI), and one or
more RLOCs for the source EID, along with their AFIs. Multiple RLOCs more RLOCs for the source EID, along with their AFIs. Multiple RLOCs
are included to ensure that at least one is in a form which will are included to ensure that at least one is in a form which will
allow the reply to be returned to the requesting ITR, and the source allow the reply to be returned to the requesting ITR, and the source
EID is used for a variety of functions, including 'gleaning' (see EID is used for a variety of functions, including 'gleaning' (see
Section 9.7). Section 9.7, " Mapping Gleaning in ETRs").
Finally, the message includes a long nonce, for simple, efficient Finally, the message includes a long nonce, for simple, efficient
protection against offpath attackers (see [Perspective], Section protection against offpath attackers (see [Perspective], Section
"Security-xTRs" for more), and a variety of other fields and control "Security-xTRs" for more), and a variety of other fields and control
flag bits. flag bits.
10.1.2. Map-Reply Messages 10.1.2. Map-Reply Messages
The Map-Reply message looks similar, except it includes the mapping The Map-Reply message looks similar, except it includes the mapping
entry for the requested EID(s), which contains one or more RLOCs and entry for the requested EID(s), which contains one or more RLOCs and
their associated data. (Note that the reply may cover a larger block their associated data. (Note that the reply may cover a larger block
of the EID namespace than the request; most requests will be for a of the EID namespace than the request; most requests will be for a
single EID, the one which prompted the query.) single EID, the one which prompted the query.)
For each RLOC in the entry, there is the RLOC, its AFI (of course), If there are no mappings available at all for the EID(s) requested, a
priority and weight fields (see Section 6.2), and multicast priority 'Negative Map-Reply' message will be returned. This is a Map-Reply
and weight fields. message with flag bits set to indicate that fact.
For each RLOC in the entry, there is the RLOC, its AFI, priority and
weight fields (see Section 6.2, " The Mapping System"), and multicast
priority and weight fields (see Section 11, "Multicast Support in
LISP"> for more about multicast support in LISP).
10.1.2.1. Solicit-Map-Request Messages 10.1.2.1. Solicit-Map-Request Messages
"Solicit-Map-Request" (SMR) messages are actually not another message "Solicit-Map-Request" (SMR) messages are actually not another message
type, but a sub-type of Map-Reply messages. They include a special type, but a sub-type of Map-Reply messages. They include a special
flag which indicates to the recipient that it _should_ send a new flag which indicates to the recipient that it _should_ send a new
Map-Request message, to refresh its mapping, because the ETR has Map-Request message, to refresh its mapping, because the ETR has
detected that the one it is using is out-dated. detected that the one it is using is out-dated.
SMR's, like most other control traffic, is rate-limited. {{Need to SMR's, like most other control traffic, is rate-limited.
say more about rate limiting, probably in security section? Ref to
that from here.}}
10.1.3. Map-Register and Map-Notify Messages 10.1.3. Map-Register and Map-Notify Messages
The Map-Register message contains authentication information, and a The Map-Register message contains authentication information, and a
number of mapping records, each with an individual Time-To-Live number of mapping records, each with an individual Time-To-Live
(TTL). Each of the records contains an EID (potentially, a block of (TTL). Each of the records contains an EID (potentially, a block of
EIDs) and its AFI, a version number for this mapping (see EIDs) and its AFI, a version number for this mapping (see
Section 9.3.1), and a number of RLOCs and their AFIs. Section 9.3.1, "Section 9.3.1 format="title"/>"), and a number of
RLOCs and their AFIs.
Each RLOC entry also includes the same data as in the Map-Replies Each RLOC entry also includes the same data as in the Map-Replies
(i.e. priority and weight); this is because in some circumstances it (i.e. priority and weight); this is because in some circumstances it
is advantageous to allow the MS to proxy reply on the ETR's behalf to is advantageous to allow the MS to proxy reply on the ETR's behalf to
Map-Request messages. [Mobility] Map-Request messages, and the MS needs this information when it does
so (see [Mobility]).
Map-Notify messages have the exact same contents as Map-Register Map-Notify messages have the exact same contents as Map-Register
messages; they are purely acknowledgements. messages; they are purely acknowledgements (although planned LISP
functionality extensions may give them other functions as well).
The entire interaction can be authenticated by use of a shared key,
configured in the MS and ETR. Although the protocol does already
allow for replacement of the encryption algorithm, it does not
support automated key management (although it appears to fall under
the exclusions in [RFC4107]).
10.2. The DDT Indexing Sub-system 10.2. The DDT Indexing Sub-system
As previously mentioned Section 6.2.3, the indexing sub-system in As previously mentioned in Section 6.2.3, "Indexing Sub-system", the
LISP is currently the DDT system. indexing sub-system in LISP is currently the DDT system.
The overall operation is fairly simple; an MR which needs a mapping The overall operation is fairly simple; an MR which needs a mapping
starts at a server for the root DDT node (there will normally be more starts at a server for the root DDT node (there will normally be more
than one such server available, for both performance and robustness than one such server available, for both performance and robustness
reasons), and through a combination of cached delegation information, reasons), and through a combination of cached delegation information,
and repetitive querying of a sequence of DDT servers, works its way and repetitive querying of a sequence of DDT servers, works its way
down the delegation tree until it arrives at an MS which is down the delegation tree until it arrives at an MS which is
authoritative (responsible?) for the block of EID namespace which authoritative (responsible?) for the block of EID namespace which
holds the destination EID in question. holds the destination EID in question.
The interaction between MRs and DDT servers is not complex; the MR The interaction between MRs and DDT servers is not complex; the MR
sends the DDT server a Map-Request control message (which looks sends the DDT server a Map-Request control message. The DDT server
almost exactly like the Map-Request which an ITR sends to an MR). uses its data (which is configured, and static) to see whether it is
The DDT server uses its data (which is configured, and static) to see directly peered to an MS which can answer the request, or if it has a
whether it is directly peered to an MS which can answer the request, child (or children, if replicated) which is responsible for that
or if it has a child (or children, if replicated) which is portion of the EID namespace.
responsible for that portion of the EID namespace.
If it has children which are responsible, it will reply to the MR If it has children configured which are responsible, it will reply to
with another kind of LISP control message, a Map-Referral message, the MR with another kind of LISP control message, a Map-Referral
which provides information about the delegation of the block message, which provides information about the delegation of the block
containing the requested EID. The Map-Referral also gives the RLOCs containing the requested EID. This process is secured; see
of all the machines which are DDT servers for that block. and the MR Section 10.4, "Security of the DDT Indexing Sub-system", for more.
can then send Map-Requests to any one (or all) of them.
The Map-Referral also gives the RLOCs of all the machines which are
DDT servers for that block. and the MR can then send Map-Requests to
any one (or all) of them. In addition, the Map-Referral includes key
data for the children, which allows any information provided by them
to be cryptographically verified.
Control flags in the Map-Referral indicate to the querying MR whether Control flags in the Map-Referral indicate to the querying MR whether
the referral is to another DDT node, an MS, or an ETR. If the the referral is to another DDT node, an MS, or an ETR. If the
former, the MR then sends the Map-Request to the child DDT node, former, the MR then sends the Map-Request to the child DDT node,
repeating the process. repeating the process.
If the latter, the MR then interacts with that MS, and usually the If the latter, the MR then interacts with that MS, and usually the
block's ETR(s) as well, to cause a mapping to be sent to the ITR block's ETR(s) as well, to cause a mapping to be sent to the ITR
which queried the MR for it. (Recall that some MS's provide Map- which queried the MR for it. (Recall that some MS's provide Map-
Replies on behalf of an associated ETR, so in such cases the Map- Replies on behalf of an associated ETR, in so-called 'proxy mode', so
Reply will come from the MS, not the ETR. {{I think this case has in such cases the Map-Reply will come from the MS, not the ETR. )
been mentioned already; check.}})
Delegations are cached in the MRs, so that once an MR has received Delegations are cached in the MRs, so that once an MR has received
information about a delegation, it will not need to look that up information about a delegation, it will not need to look that up
again. Once it has been in operation for a short while, it will only again. Once it has been in operation for a short while, it will only
need to ask for delegation information which is has not yet asked need to ask for delegation information which is has not yet asked
about - probably only the last stage in a delegation to a 'leaf' MS. about - probably only the last stage in a delegation to a 'leaf' MS.
As describe below (Section 10.6), significant amounts of modeling and As describe below (Section 10.6, "Performance of the Mapping
performance measurement have been performed, to verify that DDT has System"), significant amounts of modeling and performance measurement
(and will continue to have) acceptable performance. have been performed, to verify that DDT has (and will continue to
have) acceptable performance.
10.2.1. Map-Referral Messages 10.2.1. Map-Referral Messages
Map-Referral messages look almost identical to Map-Reply messages Map-Referral messages look almost identical to Map-Reply messages,
(which is felt to be an advantage by some people, although having a except that the RLOCs potentially name either i) other DDT nodes
more generic record-based format would probably be better in the long (children in the delegation tree), or ii) terminal MSs.
run, as ample experience with DNS has shown), except that the RLOCs
potentially name either i) other DDT nodes (children in the
delegation tree), or ii) terminal MSs.
10.3. Reliability via Replication 10.3. Reliability via Replication
Everywhere throughout the mapping system, robustness to operational Everywhere throughout the mapping system, robustness to operational
failures is obtained by replicating data in multiple instances of any failures is obtained by replicating data in multiple instances of any
particular node (of whatever type). Map-Resolvers, Map-Servers, DDT particular node (of whatever type). Map-Resolvers, Map-Servers, DDT
nodes, ETRs - all of them can be replicated, and the protocol nodes, ETRs - all of them can be replicated, and the protocol
supports this replication. supports this replication.
The deployed DDT system actually uses anycast [RFC4786], along with The deployed DDT system actually uses anycast [RFC4786], along with
replicated servers, to improve both performance and robustness. replicated servers, to improve both performance and robustness.
There are generally no mechanisms specified yet to ensure coherence There are generally no mechanisms specified yet to ensure coherence
between multiple copies of any particular data item, etc - this is between multiple copies of any particular data item (e.g. the copies
currently a manual responsibility. If and when LISP protocol of delegation data for a particular block of namespace, in DDT
adoption proceeds, an automated layer to perform this functionality sibling servers) - this is currently a manual responsibility.
can 'easily' be layered on top of the existing mechanisms.
If and when LISP protocol adoption proceeds, an automated layer to
perform this functionality can 'easily' be layered on top of the
existing mechanisms.
10.4. Security of the DDT Indexing Sub-system 10.4. Security of the DDT Indexing Sub-system
LISP provides an advanced model for securing the mapping indexing LISP provides an advanced model for securing the mapping indexing
system, in line with the overall LISP security philosophy. system, in line with the overall LISP security philosophy.
Briefly, securing the mapping indexing system is broken into two Briefly, securing the mapping indexing system is broken into two
parts: the interface between the clients of the system (MR's) and the parts: the interface between the clients of the system (MR's) and the
mapping indexing system itself, and the interaction between the DDT mapping indexing system itself, and the interaction between the DDT
nodes/servers which make it up. nodes/servers which make it up.
The client interface provides only a single model, using the The client interface provides only a single model, using the
'canonical' public-private key system (starting from a trust anchor), 'canonical' public-private key system (starting from a trust anchor),
in which the child's public key is provided by the parent, along with in which the child's public key is provided by the parent, along with
the delegation. This requires very little configuration in the the delegation. When the child returns any data, it can sign the
clients, and is fairly secure. data, and the requestor can use that signature to verify the data.
This requires very little configuration in the clients, and is fairly
secure.
The interface between the DDT nodes/servers allows for choices The interface between the DDT nodes/servers allows for choices
between a number of different options, allowing the operators to between a number of different options, allowing the operators to
trade off among configuration complexity, security level, etc. This trade off among configuration complexity, security level, etc. This
is based on experience with DNS-SEC ([RFC4033]), where configuration is based on experience with DNS-SEC ([RFC4033]), where configuration
complexity in the servers has been a major stumbling block to complexity in the servers has been a major stumbling block to
deployment. deployment.
See [Perspective], Section "Security-Mappings" for more. See [Perspective], Section "Security-Mappings" for more.
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information, would have good performance, with average resolution information, would have good performance, with average resolution
times on the order of the MR to MS RTT. This verified the times on the order of the MR to MS RTT. This verified the
effectiveness of this particular type of indexing system. effectiveness of this particular type of indexing system.
A more recent study, [Saucez], has measured actual resolution times A more recent study, [Saucez], has measured actual resolution times
in the deployed LISP network; it took measurements from a variety of in the deployed LISP network; it took measurements from a variety of
locations in the Internet, with respect to a number of different locations in the Internet, with respect to a number of different
target EIDs. Average measured resolution delays ranged from roughly target EIDs. Average measured resolution delays ranged from roughly
175 msec to 225 msec, depending on the location. 175 msec to 225 msec, depending on the location.
11. Deployment Mechanisms 11. Multicast Support in LISP
Multicast ([RFC3170], [RFC5110]) may seem an odd thing to support
with LISP, since LISP is all about separating identity from location,
and although a multicast group in some sense has an identity, it
certainly does not have _a_ location.
However, multicast is very important to some users of the network,
for a number of reasons: doing multiple unicast streams is
inefficient, as it is easy to use up all the upstream bandwidth;
without multicast a server can also be saturated fairly easily in
doing the unicast replication; etc.
So it is important for LISP to work well with multicast; doing so has
been a significant focus in LISP throughout its entire development.
Further very significant improvements to multicast support in LISP
are in progress; see [Improvements], Section "Multicast" for more on
them.
11.1. Basic Concepts of Multicast Support in LISP
This section introduces most of the basic principles of multicast
support in LISP.
Since group addresses name distributed collective entities, in
general they cannot have a single RLOC (although they may, after
future improvements in multicast support in LISP, have multiple
RLOCs); also, since they usually refer to collections of entities,
they aren't really EIDs either.
A multicast source at a LISP site may not be able to become the root
of a distribution tree in the core if it uses its EID as its identity
for that distribution tree (i.e. a distribution tree (S-EID, G));
that is because there may not be a route to its EID in the core
(assuming that its section of the core even supports multicast; not
all parts of the core do).
Therefore, outside the LISP site, multicast state for the
distribution tree (S-RLOC, G) needs to be built instead, where S-RLOC
is the RLOC of the ITR that the multicast source inside the LISP site
will be sending its traffic through.
Similarly, multicast receivers must join using the RLOC of the ETR
through which traffic will be forward to them.
Multicast LISP requires no packet format changes to existing
multicast packets (both control, and user data). The initial
multicast support in LISP uses existing multicast control mechanisms
exclusively; improvements currently being worked on provide LISP-
specific control mechanisms (see [Improvements], Section "Multicast",
for more).
11.2. Initial Multicast Support in LISP
Readers who wish to fully understand multicast support need to
consult the appropriate specifications: LISP multicast issues are
discussed in [RFC6830], Section 11; and see [RFC6831] for the full
details of current multicast support in LISP.
In the current simple operating mode (covered in [RFC6831]),
destination group addresses are not mapped; only the source address
(when the original source is inside a LISP site) needs to be mapped,
both during distribution tree setup, as well as actual traffic
delivery.
In other words, while LISP's mapping capability is used, at this
stage it is only applied to the source, not the destination (as with
most LISP activity). Thus, in LISP-encapsulated multicast packets in
this mode, the inner source is the EID, and the outer source is the
EID's RLOC; both inner and outer destinations are the group's
multicast address.
Note that this does mean that if the group is using separate source-
specific trees for distribution, there isn't a separate distribution
tree outside the LISP site for each different source of traffic to
the group from inside the LISP site; they are all lumped together
under a single source, the RLOC.
The issue of encapsulation is complex, because if the rest of the
group outside the LISP site includes some members which are at other
LISP sites (i.e. packets to them have to be encapsulated), and some
members at legacy sites (i.e. encapsulated packets would not be
understood), there is no simple answer. (The situation becomes even
more complex when one considers that as hosts leave and joint the
group, it may switch back and forth between 'mixed' and
'homogenous'.)
This issue is too complex to fully cover here; see Section 9.2.,
"LISP Sites with Mixed Address Families", in [RFC6831], for complete
coverage of this issue.
Basically, there are multicast equivalents of some of the legacy
interoperability mechanisms used for unicast; mPITRs and mPETRs
(multicast-capable PITRs and PETRs) etc. When 'mixed' groups are a
possibility, two choices are available: i) send two copies (one
encapsulated, and one not) of all traffic, or ii) employ mPETRs to
distribute non-encapsulated copies to 'legacy' group members.
12. Deployment Issues and Mechanisms
This section discusses several deployment issues in more detail. This section discusses several deployment issues in more detail.
With LISP's heavy emphasis on practicality, much work has gone into With LISP's heavy emphasis on practicality, much work has gone into
making sure it works well in the real-world environments most people making sure it works well in the real-world environments most people
have to deal with. have to deal with.
11.1. LISP Deployment Needs 12.1. LISP Deployment Needs
As mentioned earlier (Section 3.2), LISP requires no change to almost As mentioned earlier (Section 3.2, "Maximize Re-use of Existing
all existing hosts and routers. Obviously, however, one must deploy Mechanism"), LISP requires no change to almost all existing hosts and
_something_ to run LISP! Exactly what that has to be will depend routers. Obviously, however, one must deploy _something_ to run
greatly on the details of the site's existing networking gear. LISP! Exactly what that has to be will depend greatly on the details
of the site's existing networking gear, and choices it makes for how
to achieve LISP deployment.
The primary requirement is for one or more xTRs. These may be The primary requirement is for one or more xTRs. These may be
existing routers, just with new software loads, or it may require the existing routers, just with new software loads, or it may require the
deployment of new devices. deployment of new devices.
LISP also requires a small amount of LISP-specific support LISP also requires a certain amount of LISP-specific support
infrastructure, such as MRs, MSs, the DDT hierarchy, etc but much of infrastructure, such as MRs, MSs, the DDT hierarchy, etc but much of
this will either i) already be deployed, and if the new site can make this will either i) already be deployed, and if the new site can make
arrangements to use it, it need do nothing else, or ii) those arrangements to use it, it need do nothing else, or ii) those
functions it must provide may be co-located in other LISP devices functions the site must provide may be co-located in other LISP
(again, either new devices, or new software on existing ones). devices (again, either new devices, or new software on existing
ones).
11.2. Internetworking Mechanism 12.2. Interworking Mechanism
One aspect which has received a lot of attention are the mechanisms One aspect which has received a lot of attention are the mechanisms
previously referred to (in Section 4.4) to allow interoperation of previously referred to (in Section 4.4, "Interworking With Non-LISP-
LISP sites with so-called 'legacy' sites which are not running LISP Capable Endpoints") to allow interoperation of LISP sites with so-
(yet). called 'legacy' sites which are not running LISP (yet).
To briefly refresh what was said there, there are two main approaches To briefly refresh what was said there, there are two main approaches
to such interworking: proxy nodes (PITRs and PETRs), and an to such interworking: proxy nodes (PITRs and PETRs), and an
alternative mechanism using device with combined NAT and LISP alternative mechanism using device with combined NAT and LISP
functionality; these are described in more detail here. functionality; these are described in more detail here.
11.3. Proxy Devices 12.2.1. Proxy Devices
PITRs (proxy ITRs) serve as ITRs for traffic _from_ legacy hosts to PITRs (proxy ITRs) serve as ITRs for traffic _from_ legacy hosts to
nodes using LISP. PETRs (proxy ETRs) serve as ETRs for LISP traffic nodes using LISP. PETRs (proxy ETRs) serve as ETRs for LISP traffic
_to_ legacy hosts (for cases where a LISP device cannot send packets _to_ legacy hosts (for cases where a LISP device cannot send packets
directly to such hosts, without encapsulation). directly to such hosts, without encapsulation).
Note that return traffic _to_ a legacy host from a LISP-using node Note that return traffic _to_ a legacy host from a LISP-using node
does not necessarily have to pass through an ITR/PETR pair - the does not necessarily have to pass through an ITR/PETR pair - the
original packets can usually just be sent directly to the ultimate original packets can usually just be sent directly to the ultimate
destination. However, for some kinds of LISP operation (e.g. mobile destination. However, for some kinds of LISP operation (e.g. mobile
nodes), this is not possible; in these situations, the PETR is nodes), this is not possible; in these situations, the PETR is
needed. needed.
11.3.1. PITRs 12.2.1.1. PITRs
PITRs (proxy ITRs) serve as ITRs for traffic _from_ legacy hosts to PITRs (proxy ITRs) serve as ITRs for traffic _from_ legacy hosts to
nodes using LISP. To do that, they have to advertise into the nodes using LISP. To do that, they have to advertise into the
existing legacy backbone Internet routing the availability of existing legacy backbone Internet routing the availability of
whatever ranges of EIDs (i.e. of nodes using LISP) they are proxying whatever ranges of EIDs (i.e. of nodes using LISP) they are proxying
for, so that legacy hosts will know where to send traffic to those for, so that legacy hosts will know where to send traffic to those
LISP nodes. LISP nodes.
As mentioned previously (Section 9.1), an ITR at another LISP site As mentioned previously (Section 9.1, "When to Encapsulate"), an ITR
can avoid using a PITR (i.e. it can detect that a given ultimate at another LISP site can avoid using a PITR (i.e. it can detect that
destination is not a legacy host, if a PITR is advertising it into a given ultimate destination is not a legacy host, if a PITR is
the DFZ) by checking to see if a LISP mapping exists for that advertising it into the DFZ) by checking to see if a LISP mapping
ultimate destination. exists for that ultimate destination.
This technique obviously has an impact on routing table in the DFZ, This technique obviously has an impact on routing table in the DFZ,
but it is not clear yet exactly what that impact will be; it is very but it is not clear yet exactly what that impact will be; it is very
dependent on the collected details of many individual deployment dependent on the collected details of many individual deployment
decisions. decisions.
A PITR may cover a group of EID blocks with a single EID A PITR may cover a group of EID blocks with a single EID
advertisement, in order to reduce the number of routing table entries advertisement, in order to reduce the number of routing table entries
added. (In fact, at the moment, aggressive aggregation of EID added. (In fact, at the moment, aggressive aggregation of EID
announcements is performed, precisely to to minimize the number of announcements is performed, precisely to to minimize the number of
new announced routes added by this technique.) new announced routes added by this technique.)
At the same time, if a site does traffic engineering with LISP At the same time, if a site does traffic engineering with LISP
instead of fine-grained BGP announcement, that will help keep table instead of fine-grained BGP announcement, that will help keep table
sizes down (and this is true even in the early stages of LISP sizes down (and this is true even in the early stages of LISP
deployment). The same is true for multi-homing. deployment). The same is true for multi-homing.
11.3.2. PETRs 12.2.1.2. PETRs
PETRs (proxy ETRs) serve as ETRs for LISP traffic _to_ legacy hosts, PETRs (proxy ETRs) serve as ETRs for LISP traffic _to_ legacy hosts,
for cases where a LISP device cannot send packets to such hosts for cases where a LISP device cannot send packets to such hosts
without encapsulation. That typically happens for one of two without encapsulation. That typically happens for one of two
reasons. reasons.
First, it will happen in places where some device is implementing First, it will happen in places where some device is implementing
Unicast Reverse Path Forwarding (uRPF), to prevent a variety of Unicast Reverse Path Forwarding (uRPF), to prevent a variety of
negative behaviour; originating packets with the original source's negative behaviour; originating packets with the original source's
EID in the source address field will result in them being filtered EID in the source address field will result in them being filtered
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normal ETRS, PETRs do not have to register themselves in the mapping normal ETRS, PETRs do not have to register themselves in the mapping
database, on behalf of any legacy sites they serve. database, on behalf of any legacy sites they serve.
Also, allowing an ITR to always send traffic leaving a site to a PETR Also, allowing an ITR to always send traffic leaving a site to a PETR
does avoid having to chose whether or not to encapsulate packets; it does avoid having to chose whether or not to encapsulate packets; it
can just always encapsulate packets, sending them to the PETR if it can just always encapsulate packets, sending them to the PETR if it
has no specific mapping for the ultimate destination. However, this has no specific mapping for the ultimate destination. However, this
is not advised: as mentioned, it is easy to tell if something is a is not advised: as mentioned, it is easy to tell if something is a
legacy destination. legacy destination.
11.4. LISP-NAT 12.2.2. LISP-NAT
A LISP-NAT device, as previously mentioned, combines LISP and NAT A LISP-NAT device, as previously mentioned, combines LISP and NAT
functionality, in order to allow a LISP site which is internally functionality, in order to allow a LISP site which is internally
using addresses which cannot be globally routed to communicate with using addresses which cannot be globally routed to communicate with
non-LISP sites elsewhere in the Internet. (In other words, the non-LISP sites elsewhere in the Internet. (In other words, the
technique used by the PITR approach simply cannot be used in this technique used by the PITR approach simply cannot be used in this
case.) case.)
To do this, a LISP-NAT performs the usual NAT functionality, and To do this, a LISP-NAT performs the usual NAT functionality, and
translates a host's source address(es) in packets passing through it translates a host's source address(es) in packets passing through it
from an 'inner' value to an 'outer' value, and storing that from an 'inner' value to an 'outer' value, and storing that
translation in a table, which it can use to similarly process translation in a table, which it can use to similarly process
subsequent packets (both outgoing and incoming). [Interworking] subsequent packets (both outgoing and incoming). [RFC6832]
There are two main cases where this might apply: There are two main cases where this might apply:
- Sites using non-routable global addresses - Sites using non-routable global addresses
- Sites using private addresses [RFC1918] - Sites using private addresses [RFC1918]
11.5. Use Through NAT Devices 12.3. Use Through NAT Devices
Like them or not (and NAT devices have many egregious issues - some Like them or not (and NAT devices have many egregious issues - some
inherent in the nature of the process of mapping addresses; others, inherent in the nature of the process of mapping addresses; others,
such as the brittleness due to non-replicated critical state, caused such as the brittleness due to non-replicated critical state, caused
by the way NATs were introduced, as stand-alone 'invisible' boxes), by the way NATs were introduced, as stand-alone 'invisible' boxes),
NATs are both ubiquitous, and here to stay for a long time to come. NATs are both ubiquitous, and here to stay for a long time to come.
[RFC1631] Thus, in the actual Internet of today, having any new
mechanisms function well in the presence of NATs (i.e. with LISP xTRs
behind a NAT device) is absolutely necessary.
Thus, in the actual Internet of today, having any new mechanisms LISP has produced a variety of mechanisms to do this. The earliest
function well in the presence of NATs (i.e. with LISP xTRs behind a mechanism to support them had major limitations; it, and its
NAT device) is absolutely necessary. LISP has produced a variety of limitations, are described in Appendix B.5, "Early NAT Support". A
mechanisms to do this. more recent proposed mechanism, which avoids those limitations, is
described in [Improvements], Section "Improved NAT Support".
11.5.1. First-Phase NAT Support
The first mechanism used by LISP to operate through a NAT device only
worked with some NATs, those which were configurable to allow inbound
packet traffic to reach a configured host.
A pair of new LISP control messages, LISP Echo-Request and Echo-
Reply, allowed the ETR to discover its temporary global address; the
Echo-Request was sent to the configured Map-Server, and it replied
with an Echo-Reply which included the source address from which the
Echo Request was received (i.e. the public global address assigned to
the ETR by the NAT). The ETR could then insert that address in any
Map-Reply control messages which it sent to correspondent ITRs.
The fact that this mechanism did not support all NATs, and also
required manual configuration of the NAT, meant that this was not a
good solution; in addition, since LISP expects all incoming data
traffic to be on a specific port, it was not possible to have
multiple ETRs behind a single NAT (which normally would have only one
global address to share, meaning port mapping would have to be used,
except that... )
11.5.2. Second-Phase NAT Support
For a more comprehensive approach to support of LISP xTR deployment
behind NAT devices, a fairly extensive supplement to LISP, LISP NAT
Traversal, has been designed. [LISP-NAT]
A new class of LISP device, the LISP Re-encapsulating Tunnel Router
(RTR), passes traffic through the NAT, both to and from the xTR.
(Inbound traffic has to go through the RTR as well, since otherwise
multiple xTRs could not operate behind a single NAT, for the
'specified port' reason in the section above.)
(Had the Map-Reply included a port number, this could have been
avoided - although of course it would be possible to define a new
RLOC type which included protocol and port, to allow other
encapsulation techniques.)
Two new LISP control messages (Info-Request and Info-Reply) allow an
xTR to detect if it is behind a NAT device, and also discover the
global IP address and UDP port assigned by the NAT to the xTR. A
modification to LISP Map-Register control messages allows the xTR to
initialize mapping state in the NAT, in order to use the RTR.
This mechanism addresses cases where the xTR is behind a NAT, but the
xTR's associated MS is on the public side of the NAT; this
limitation, that MS's must be in the 'public' part of the Internet,
seems reasonable.
11.6. LISP and DFZ Routing 12.4. LISP and DFZ Routing
One of LISP's original motivations was to try and control the growth One of LISP's original motivations was to try and control the growth
of the size of the so-called 'Default-Free-Zone' (DFZ), the core of of the size of the so-called 'Default-Free-Zone' (DFZ), the core of
the Internet, the part where routes to _all_ destinations must be the Internet, the part where routes to _all_ destinations must be
available. As LISP becomes more widely deployed, it can help with available. As LISP becomes more widely deployed, it can help with
this issue, in a variety of ways. this issue, in a variety of ways.
In covering this topic, one must recognize that conditions in various In covering this topic, one must recognize that conditions in various
stages of LISP deployment (in terms of ubiquity) will have a large stages of LISP deployment (in terms of ubiquity) will have a large
influence. [Deployment] introduced useful terminology for this influence. [Deployment] introduced useful terminology for this
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In the early phases of deployment, two primary effects will allow In the early phases of deployment, two primary effects will allow
LISP to have a positive impact on the routing table growth: LISP to have a positive impact on the routing table growth:
- Using LISP for traffic engineering instead of BGP - Using LISP for traffic engineering instead of BGP
- Aggregation of smaller PI sites into a single PITR advertisement - Aggregation of smaller PI sites into a single PITR advertisement
The first is fairly obvious (doing TE with BGP requires injecting The first is fairly obvious (doing TE with BGP requires injecting
more-specific routes into the DFZ routing tables, something doing TE more-specific routes into the DFZ routing tables, something doing TE
with LISP avoids); the second is not guaranteed to happen (since it with LISP avoids); the second is not guaranteed to happen (since it
requires coordination among a number of different parties), and only requires coordination among a number of different parties), and only
time will tell if it does happen. time will tell if it does happen.
11.6.1. Long-term Possibilities 12.4.1. Long-term Possibilities
At a later stage of the deployment, a more aggressive approach At a later stage of the deployment, a more aggressive approach
becomes available: taking part of the DFZ, one for which all 'stub' becomes available: taking part of the DFZ, one for which all 'stub'
sites connected to it have deployed LISP, and removing all 'EID sites connected to it have deployed LISP, and removing all 'EID
routes' (used for backwards compatability with 'legacy' sites); only routes' (used for backwards compatability with 'legacy' sites); only
RLOC routes would remain in the routing table in that part of the RLOC routes would remain in the routing table in that part of the
Internet backbone. Internet backbone.
Obviously there would be a boundary between the two parts of the DFZ, Obviously there would be a boundary between the two parts of the DFZ,
and the routers on the border would have to (effectively) become and the routers on the border would have to (effectively) become
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RLOC DFZ, but re-created on crossing the boundary _out_ of the RLOC RLOC DFZ, but re-created on crossing the boundary _out_ of the RLOC
DFZ. This is likely to be impractical, leading to the suggestion of DFZ. This is likely to be impractical, leading to the suggestion of
a simpler boundary between the RLOC-only part of the DFZ, and the a simpler boundary between the RLOC-only part of the DFZ, and the
'legacy' DFZ. 'legacy' DFZ.
The mechanism for detecting which routes are 'EID routes' and which The mechanism for detecting which routes are 'EID routes' and which
are 'RLOC routes' (required for the boundary routers to be able to are 'RLOC routes' (required for the boundary routers to be able to
filter out the 'EID routes') would also need to be worked out; the filter out the 'EID routes') would also need to be worked out; the
most likely appears to be something involving BGP attributes. most likely appears to be something involving BGP attributes.
12. Fault Discovery/Handling 13. Fault Discovery/Handling
LISP is, in terms of its functionality, a fairly simple system: the LISP is, in terms of its functionality, a fairly simple system: the
list of failure modes is thus not extensive. list of failure modes is thus not extensive.
12.1. Handling Missing Mappings 13.1. Handling Missing Mappings
Handling of missing mappings is fairly simple: the ITR calls for the Handling of missing mappings is fairly simple: the ITR calls for the
mapping, and in the meantime can either discard traffic to that mapping, and in the meantime can either discard traffic to that
ultimate destination (as many ARP implementations do) [RFC826], or, ultimate destination (as many ARP implementations do) [RFC826], or,
if dropping the traffic is deemed undesirable, it can forward them if dropping the traffic is deemed undesirable, it can forward them
via a 'default PITR'. via a 'default PITR'.
A number of PITRs advertise all EID blocks into the backbone routing, A number of PITRs advertise all EID blocks into the backbone routing,
so that any ITRs which are temporarily missing a mapping can forward so that any ITRs which are temporarily missing a mapping can forward
the traffic to these default PITRs via normal transmission methods, the traffic to these default PITRs via normal transmission methods,
where they are encapsulated and passed on. where they are encapsulated and passed on.
12.2. Outdated Mappings 13.2. Outdated Mappings
If a mapping changes once an ITR has retrieved it, that may result in If a mapping changes once an ITR has retrieved it, that may result in
traffic to the EIDs covered by that mapping failing. There are three traffic to the EIDs covered by that mapping failing. There are three
cases to consider: cases to consider:
- When the ETR traffic is being sent to is still a valid ETR for - When the ETR traffic is being sent to is still a valid ETR for
that EID, but the mapping has been updated (e.g. to change the that EID, but the mapping has been updated (e.g. to change the
priority of various ETRs) priority of various ETRs)
- When the ETR traffic is being sent to is still an ETR, but no - When the ETR traffic is being sent to is still an ETR, but no
longer a valid ETR for that EID longer a valid ETR for that EID
- When the ETR traffic is being sent to is no longer an ETR - When the ETR traffic is being sent to is no longer an ETR
12.2.1. Outdated Mappings - Updated Mapping 13.2.1. Outdated Mappings - Updated Mapping
A 'mapping versioning' system, whereby mappings have version numbers, A 'mapping versioning' system, whereby mappings have version numbers,
and ITRs are notified when their mapping is out of date, has been and ITRs are notified when their mapping is out of date, has been
added to detect this, and the ITR responds by refreshing the mapping. added to detect this, and the ITR responds by refreshing the mapping.
[Versioning] [RFC6834]
12.2.2. Outdated Mappings - Wrong ETR 13.2.2. Outdated Mappings - Wrong ETR
If an ITR is holding a seriously outdated cached mapping, it may send If an ITR is holding an outdated cached mapping, it may send packets
packets to an ETR which is no longer an ETR for that EID. to an ETR which is no longer an ETR for that EID.
It might be argued that if the ETR is properly managing the lifetimes It might be argued that if the ETR is properly managing the lifetimes
on its mapping entries, this 'cannot happen', but it is a wise design on its mapping entries, this 'cannot happen', but it is a wise design
methodology to assume that 'cannot happen' events will in fact happen methodology to assume that 'cannot happen' events will in fact happen
(as they do, due to software errors, or, on rare occasions, hardware (as they do, due to software errors, or, on rare occasions, hardware
faults), and ensure that the system will handle them properly (if, faults), and ensure that the system will handle them properly (if,
perhaps not in the most expeditious, or 'clean' way - they are, after perhaps not in the most expeditious, or 'clean' way - they are, after
all, very unlikely to happen). all, very unlikely to happen).
ETRs can easily detect cases where this happpens, after they have un- ETRs can easily detect cases where this happpens, after they have un-
wrapped a user data packet; in response, they send a Solicit-Map- wrapped a user data packet; in response, they send a Solicit-Map-
Request to the source ITR to cause it to refresh its mapping. Request to the source ITR to cause it to refresh its mapping.
12.2.3. Outdated Mappings - No Longer an ETR 13.2.3. Outdated Mappings - No Longer an ETR
In another case for what can happen if an ITR uses an outdated In another case for what can happen if an ITR uses an outdated
mapping, the destination of traffic from an ITR might no longer be a mapping, the destination of traffic from an ITR might no longer be a
LISP device at all. In such cases, one might get an ICMP Destination LISP device at all. In such cases, one might get an ICMP Destination
Unreachable error message. However, one cannot depend on that - and Unreachable error message. However, one cannot depend on that - and
in any event, that would provide an attack vector, so it should be in any event, that would provide an attack vector, so it should be
used with care. (See [LISP], Section 6.3, "Routing Locator used with care. (See [RFC6830], Section 6.3, "Routing Locator
Reachability" for more about this.) Reachability" for more about this.)
The following mechanism will work, though. Since the destination is The following mechanism will work, though. Since the destination is
not an ETR, the echoing reachability detection mechanism (see not an ETR, the echoing reachability detection mechanism (see
Section 9.3.2) will detect a problem. At that point, the backstop Section 9.3.2, "Echo Nonces") will detect a problem. At that point,
mechanism, Probing, will kick in. Since the destination is still not the backstop mechanism, Probing, will kick in. Since the destination
an ETR, that will fail, too. is still not an ETR, that will fail, too.
At that point, traffic will be switched to a different ETR, or, if At that point, traffic will be switched to a different ETR, or, if
none are available, a reload of the mapping may be initiated. none are available, a reload of the mapping may be initiated.
12.3. Erroneous Mappings 13.3. Erroneous Mappings
Again, this 'should not happen', but a good system should deal with Again, this 'should not happen', but a good system should deal with
it. However, in practise, should this happen, it will produce one of it. However, in practise, should this happen, it will produce one of
the prior two cases (the wrong ETR, or something that is not an ETR), the prior two cases (the wrong ETR, or something that is not an ETR),
and will be handled as described there. and will be handled as described there.
12.4. Neighbour Liveness 13.4. Neighbour ETR Liveness
The ITR, like all packet switches, needs to detect, and react, when The ITR, like all packet switches, needs to detect, and react, when
its next-hop neighbour ceases operation. As LISP traffic is its neighbour ceases operation. As LISP traffic is effectively
effectively always unidirectional (from ITR to ETR), this could be always uni-directional (from ITR to ETR), this could be somewhat
somewhat problematic. problematic.
Solving a related problem, neighbour reachability (below) subsumes Solving a related problem, neighbour ETR reachability (below)
handling this fault mode, however. subsumes handling this fault mode, however.
Note that the two terms (liveness and reachability) are _not_ Note that the two terms - liveness and reachability - are _not_
synonmous (although a lot of LISP documentation confuses them). synonmous (although they are often confused). Liveness is a property
Liveness is a property of a node - it is either up and functioning, of a node - it is either up and functioning, or it is not.
or it is not. Reachability is only a property of a particular _pair_ Reachability is only a property of a particular _pair_ of nodes.
of nodes.
If packets sent from a first node to a second are successfully If packets sent from a first node to a second are successfully
received at the second, it is 'reachable' from the first. However, received at the second, it is 'reachable' from the first. However,
the second node may at the very same time _not_ be reachable from the second node may at the very same time _not_ be reachable from
some other node. Reachability is _always_ a ordered pairwise some other node. Reachability is _always_ a ordered pairwise
property, and of a specified ordered pair. property, and of a specified ordered pair.
12.5. Neighbour Reachability 13.5. Neighbour ETR Reachability
A more significant issue than whether a particular ETR E is up or not A more significant issue than whether a particular ETR E is up or not
is, as mentioned above, that although ETR E may be up, attached to is, as mentioned above, that although ETR E may be up, attached to
the network, etc, an issue in the network between a source ITR I and the network, etc, an issue in the network, between a source ITR I and
E may prevent traffic from I from getting to E. (Perhaps a routing E, may prevent traffic from I from getting to E. (Perhaps a routing
problem, or perhaps some sort of access control setting.) problem, or perhaps some sort of access control setting.)
The one-way nature of LISP traffic makes this situation hard to The one-way nature of LISP traffic makes this situation hard to
detect in a way which is economic, robust and fast. Two out of the detect in a way which is economic, robust and fast. Two out of the
three are usually not to hard, but all three at the same time - as is three are usually not to hard, but all three at the same time - as is
highly desirable for this particular issue - are harder. highly desirable for this particular issue - are harder.
In line with the LISP design philosophy ([Perspective], Section In line with the LISP design philosophy ([Perspective], Section
"Design-Theoretical"), this problem is attacked not with a single "Design-Theoretical"), this problem is attacked not with a single
mechanism (which would have a hard time meeting all those three goals mechanism (which would have a hard time meeting all those three goals
skipping to change at line 1844 skipping to change at page 45, line 21
They are reliance on the underlying routing system (which can of They are reliance on the underlying routing system (which can of
course only reliably provide a negative reachabilty indication, not a course only reliably provide a negative reachabilty indication, not a
positive one), the echo nonce (which depends on some return traffic positive one), the echo nonce (which depends on some return traffic
from the destination xTR back to the source xTR), and finally direct from the destination xTR back to the source xTR), and finally direct
'pinging', in the case where no positive echo is returned. 'pinging', in the case where no positive echo is returned.
(The last is not the first choice, as due to the large fan-out (The last is not the first choice, as due to the large fan-out
expected of LISP devices, reliance on it as a sole mechanism would expected of LISP devices, reliance on it as a sole mechanism would
produce a fair amount of overhead.) produce a fair amount of overhead.)
13. Current Improvements
In line with the philosophies laid out in Section 8, LISP is
something of a moving target. This section discusses some of the
contemporaneous improvements being made to LISP.
13.1. Improved NAT Support
13.2. Mobile Device Support
Mobility is an obvious capability to provide with LISP. Doing so is
relatively simple, if the mobile host is prepared to act as its own
ETR. It obtains a local 'temporary use' address, and registers that
address as its RLOC. Packets to the mobile host are sent to its
temporary address, wherever that may be, and the mobile host first
unwraps them (acting as an ETR), and the processes them normally
(acting as a host).
(Doing mobility without having the mobile host act as its ETR is
difficult, even if ETRs are quite common. The reason is that if the
ETR and mobile host are not integrated, during the step from the ETR
to the mobile host, the packets must contain the mobile host's EID,
and this may not be workable. If there is a local router between the
ETR and mobile host, for instance, it is unlikely to know how to get
the packets to the mobile host.)
If the mobile host migrates to a site which is itself a LISP site,
things get a little more complicated. The 'temporary address' it
gets is itself an EID, requiring mapping, and wrapping for transit
across the rest of the Internet. A 'double encapsulation' is thus
required at the other end; the packets are first encapsulated with
the mobile node's temporary address as their RLOC, and then this has
to be looked up in a second lookup cycle (see Section 9.1), and then
wrapped again, with the site's RLOC as their destination.
This results in slight loss in maximum packet size, due to the
duplicated headers, but on the whole it is considerably simpler than
the alternative, which would be to re-wrap the packet at the site's
ETR, when it is discovered that the ultimate destination's EID was
not 'native' to the site. This would require that the mobile node's
EID effectively have two different mappings, depending on whether the
lookup was being performed outside the LISP site, or inside.
{{Also probably need to mention briefly how the other end is notified
when mappings are updated, and about proxy-Map-Replies.}} [Mobility]
13.3. Multicast Support
Multicast may seem an odd thing to support with LISP, since LISP is
all about separating identity from location, but although a multicast
group in some sense has an identity, it certainly does not have _a_
location.
However, multicast is important to some users of the network, for a
number of reasons: doing multiple unicast streams is inefficient; it
is easy to use up all the upstream bandwidth, and without multicast a
server can also be saturated fairly easily in doing the unicast
replication. So it is important for LISP to 'play nicely' with
multicast; work on multicast support in LISP is fairly advanced,
although not far-ranging.
Briefly, destination group addresses are not mapped; only the source
address (when the original source is inside a LISP site) needs to be
mapped, both during distribution tree setup, as well as actual
traffic delivery. In other words, LISP's mapping capability is used:
it is just applied to the source, not the destination (as with most
LISP activity); the inner source is the EID, and the outer source is
the EID's RLOC.
Note that this does mean that if the group is using separate source-
specific trees for distribution, there isn't a separate distribution
tree outside the LISP site for each different source of traffic to
the group from inside the LISP site; they are all lumped together
under a single source, the RLOC.
The approach currently used by LISP requires no packet format changes
to existing multicast protocols. See [Multicast] for more;
additional LISP multicast issues are discussed in [LISP], Section 12.
13.4. {{Any others?}}
14. Acknowledgments 14. Acknowledgments
The author would like to start by thanking all the members of the The author would like to start by thanking all the members of the
core LISP group for their willingness to allow him to add himself to core LISP group for their willingness to allow him to add himself to
their effort, and for their enthusiasm for whatever assistance he has their effort, and for their enthusiasm for whatever assistance he has
been able to provide. been able to provide.
He would also like to thank (in alphabetical order) Vina Ermagan, He would also like to thank (in alphabetical order) Michiel Blokzijl,
Vince Fuller and Vasileios Lakafosis for their careful review of, and Peter Chiappa, Vina Ermagan, Dino Farinacci, Vince Fuller and
helpful suggestions for, this document. (If I have missed anyone in Vasileios Lakafosis for their review of, and helpful suggestions for,
this list, I apologize most profusely.) A very special thank you this document. (If I have missed anyone in this list, I apologize
goes to Joel Halpern, who, when asked, promptly returned comments on most profusely.)
intermediate versions of this document. Grateful thanks go also to
Darrel Lewis for his help with material on non-Internet uses of LISP, A very special thank you goes to Joel Halpern, who almost invariably,
and to Vince Fuller and Dino Farinacci for answering detailed when asked, promptly returned comments on intermediate versions of
questions about some obscure LISP topics. this document. Grateful thanks go also to Darrel Lewis for his help
with material on non-Internet uses of LISP, and to Dino Farinacci and
Vince Fuller for answering detailed questions about some obscure LISP
topics.
A final thanks is due to John Wrocklawski for the author's A final thanks is due to John Wrocklawski for the author's
organizational affiliation, and to Vince Fuller for help with XML. organizational affiliation, and to Vince Fuller for help with XML.
This memo was created using the xml2rfc tool. This memo was created using the xml2rfc tool.
I would like to dedicate this document to the memory of my parents, I would like to dedicate this document to the memory of my parents,
who gave me so much, and whom I can no longer thank in person, as I who gave me so much, and whom I can no longer thank in person, as I
would have so much liked to be able to. would have so much liked to be able to.
15. IANA Considerations 15. IANA Considerations
skipping to change at line 1963 skipping to change at page 46, line 14
16. Security Considerations 16. Security Considerations
This memo does not define any protocol and therefore creates no new This memo does not define any protocol and therefore creates no new
security issues. security issues.
17. References 17. References
17.1. Normative References 17.1. Normative References
[RFC768] J. Postel, "User Datagram Protocol", RFC 768, [AFI] IANA, "Address Family Indicators (AFIs)", Address
August 1980. Family Numbers, January 2011, <http://www.iana.org/
assignments/address-family-numbers>.
[RFC791] J. Postel, "Internet Protocol", RFC 791, [RFC768] J. Postel, "User Datagram Protocol", RFC 768,
September 1981. August 1980.
[RFC1498] J. H. Saltzer, "On the Naming and Binding of Network [RFC791] J. Postel, "Internet Protocol", RFC 791,
Destinations", RFC 1498, (Originally published in: September 1981.
"Local Computer Networks", edited by P. Ravasio et
al., North-Holland Publishing Company, Amsterdam,
1982, pp. 311-317.), August 1993.
[RFC2460] S. Deering and R. Hinden, "Internet Protocol, Version [RFC2460] S. Deering and R. Hinden, "Internet Protocol,
6 (IPv6) Specification", RFC 2460, December 1998. Version 6 (IPv6) Specification", RFC 2460,
December 1998.
[AFI] IANA, "Address Family Indicators (AFIs)", Address [RFC6830] D. Farinacci, V. Fuller, D. Meyer, and D. Lewis,
Family Numbers, January 2011, <http://www.iana.org/ "The Locator/ID Separation Protocol (LISP)",
assignments/address-family-numbers>. RFC 6830, January 2013.
[LISP] D. Farinacci, V. Fuller, D. Meyer, and D. Lewis, "The [RFC6831] D. Farinacci, D. Meyer, J. Zwiebel, and S. Venaas,
Locator/ID Separation Protocol (LISP)", RFC 6830, "The Locator/ID Separation Protocol (LISP) for
January 2013. Multicast Environments", RFC 6831, January 2013.
[MapInterface] V. Fuller and D. Farinacci, "Locator/ID Separation [RFC6832] D. Lewis, D. Meyer, D. Farinacci, and V. Fuller,
Protocol (LISP) Map-Server Interface", RFC 6833, "Interworking between Locator/ID Separation Protocol
January 2013. (LISP) and Non-LISP Sites", RFC 6832, January 2013.
[Versioning] L. Iannone, D. Saucez, and O. Bonaventure, [RFC6833] V. Fuller and D. Farinacci, "Locator/ID Separation
"Locator/ID Separation Protocol (LISP) Map- Protocol (LISP) Map-Server Interface", RFC 6833,
Versioning", RFC 6834, January 2013. January 2013.
[Interworking] D. Lewis, D. Meyer, D. Farinacci, and V. Fuller, [RFC6834] L. Iannone, D. Saucez, and O. Bonaventure,
"Interworking between Locator/ID Separation Protocol "Locator/ID Separation Protocol (LISP) Map-
(LISP) and Non-LISP Sites", RFC 6832, January 2013. Versioning", RFC 6834, January 2013.
[DDT] V. Fuller, D. Lewis, and D. Farinacci, "LISP [Perspective] J. N. Chiappa, "An Architectural Perspective on the
Delegated Database Tree", draft-ietf-lisp-ddt-00 LISP Location-Identity Separation System",
(work in progress), October 2012. draft-ietf-lisp-perspective-00 (work in progress),
February 2013.
[Perspective] J. N. Chiappa, "An Architectural Perspective on the [Improvements] J. N. Chiappa, "An Overview of On-Going Improvements
LISP Location-Identity Separation System", to the LISP Location-Identity Separation System",
draft-ietf-lisp-perspective-00 (work in progress), draft-chiappa-lisp-improvements-00 (work in
February 2013. progress), September 2013.
[Future] J. N. Chiappa, "Potential Long-Term Developments With [DDT] V. Fuller, D. Lewis, and D. Farinacci, "LISP
the LISP System", draft-chiappa-lisp-evolution-00 Delegated Database Tree", draft-ietf-lisp-ddt-01
(work in progress), October 2012. (work in progress), March 2013.
[LISP-SEC] F. Maino, V. Ermagan, A. Cabellos-Aparicio, [LISP-SEC] F. Maino, V. Ermagan, A. Cabellos-Aparicio,
D. Saucez, and O. Bonaventure, "LISP-Security (LISP- D. Saucez, and O. Bonaventure, "LISP-Security (LISP-
SEC)", draft-ietf-lisp-sec-04 (work in progress), SEC)", draft-ietf-lisp-sec-04 (work in progress),
October 2012. October 2012.
[LISP-NAT] V. Ermagan, D. Farinacci, D. Lewis, J. Skriver, [NAT-Traversal] V. Ermagan, D. Farinacci, D. Lewis, J. Skriver,
F. Maino, and C. White, "NAT traversal for LISP", F. Maino, and C. White, "NAT traversal for LISP",
draft-ermagan-lisp-nat-traversal-03 (work in draft-ermagan-lisp-nat-traversal-03 (work in
progress), March 2013. progress), March 2013.
[Mobility] D. Farinacci, V. Fuller, D. Lewis, and D. Meyer, [Mobility] D. Farinacci, V. Fuller, D. Lewis, and D. Meyer,
"LISP Mobility Architecture", draft-meyer-lisp-mn-07 "LISP Mobility Architecture", draft-meyer-lisp-mn-08
(work in progress), April 2012. (work in progress), April 2012.
[Multicast] D. Farinacci, D. Meyer, J. Zwiebel, and S. Venaas, [Deployment] L. Jakab, A. Cabellos-Aparicio, F. Coras,
"The Locator/ID Separation Protocol (LISP) for J. Domingo-Pascual, and D. Lewis, "LISP Network
Multicast Environments", RFC 6831, January 2013. Element Deployment Considerations",
draft-ietf-lisp-deployment-09 (work in progress),
July 2013.
[Deployment] L. Jakab, A. Cabellos-Aparicio, F. Coras, J. Domingo- [LISP-TE] D. Farinacci, P. Lahiri, and M. Kowal, "LISP Traffic
Pascual, and D. Lewis, "LISP Network Element Engineering Use-Cases", draft-farinacci-lisp-te-03
Deployment Considerations", (work in progress), July 2013.
draft-ietf-lisp-deployment-08 (work in progress),
June 2013.
17.2. Informative References 17.2. Informative References
[NIC8246] A. McKenzie and J. Postel, "Host-to-Host Protocol for [NIC8246] A. McKenzie and J. Postel, "Host-to-Host Protocol
the ARPANET", NIC 8246, Network Information Center, for the ARPANET", NIC 8246, Network Information
SRI International, Menlo Park, CA, October 1977. Center, SRI International, Menlo Park, CA,
October 1977.
[IEN19] J. F. Shoch, "Inter-Network Naming, Addressing, and [NSAP] International Organization for Standardization,
Routing", IEN (Internet Experiment Note) 19, "Information Processing Systems - Open Systems
January 1978. Interconnection - Basic Reference Model", ISO
Standard 7489.1984, 1984.
[RFC826] D. Plummer, "Ethernet Address Resolution Protocol", [IEN19] J. F. Shoch, "Inter-Network Naming, Addressing, and
RFC 826, November 1982. Routing", IEN (Internet Experiment Note) 19,
January 1978.
[RFC1034] P. V. Mockapetris, "Domain Names - Concepts and [RFC826] D. Plummer, "Ethernet Address Resolution Protocol",
Facilities", RFC 1034, November 1987. RFC 826, November 1982.
[RFC1631] K. Egevang and P. Francis, "The IP Network Address [RFC1034] P. V. Mockapetris, "Domain Names - Concepts and
Translator (NAT)", RFC 1631, May 1994. Facilities", RFC 1034, November 1987.
[RFC1918] Y. Rekhter, R. Moskowitz, D. Karrenberg, [RFC1498] J. H. Saltzer, "On the Naming and Binding of Network
G. J. de Groot, and E. Lear, "Address Allocation for Destinations", RFC 1498, (Originally published in:
Private Internets", RFC 1918, February 1996. 'Local Computer Networks', edited by P. Ravasio et
al., North-Holland Publishing Company, Amsterdam,
1982, pp. 311-317.), August 1993.
[RFC1992] I. Castineyra, J. N. Chiappa, and M. Steenstrup, "The [RFC1631] K. Egevang and P. Francis, "The IP Network Address
Nimrod Routing Architecture", RFC 1992, August 1996. Translator (NAT)", RFC 1631, May 1994.
[RFC3168] K. Ramakrishnan, S. Floyd, and D. Black, "The [RFC1918] Y. Rekhter, R. Moskowitz, D. Karrenberg,
Addition of Explicit Congestion Notification (ECN) to G. J. de Groot, and E. Lear, "Address Allocation for
IP", RFC 3168, September 2001. Private Internets", RFC 1918, February 1996.
[RFC3272] D. Awduche, A. Chiu, A. Elwalid, I. Widjaja, and [RFC1992] I. Castineyra, J. N. Chiappa, and M. Steenstrup,
X. Xiao, "Overview and Principles of Internet Traffic "The Nimrod Routing Architecture", RFC 1992,
Engineering", RFC 3272, May 2002. August 1996.
[RFC4026] L. Andersson and T. Madsen, "Provider Provisioned [RFC3168] K. Ramakrishnan, S. Floyd, and D. Black, "The
Virtual Private Network (VPN) Terminology", RFC 4026, Addition of Explicit Congestion Notification (ECN)
March 2005. to IP", RFC 3168, September 2001.
[RFC4033] R. Arends, R. Austein, M. Larson, D. Massey, and [RFC3170] B. Quinn and K. Almeroth, "IP Multicast
S. Rose, "DNS Security Introduction and Applications: Challenges and Solutions", RFC 3170,
Requirements", RFC 4033, March 2005. September 2001.
[RFC4116] J. Abley, K. Lindqvist, E. Davies, B. Black, and [RFC3272] D. Awduche, A. Chiu, A. Elwalid, I. Widjaja, and
V. Gill, "IPv4 Multihoming Practices and X. Xiao, "Overview and Principles of Internet
Limitations", RFC 4116, July 2005. Traffic Engineering", RFC 3272, May 2002.
[RFC4786] J. Abley and K. Lindqvist, "Operation of Anycast [RFC4026] L. Andersson and T. Madsen, "Provider Provisioned
Services", RFC 4786, December 2006. Virtual Private Network (VPN) Terminology",
RFC 4026, March 2005.
[RFC4984] D. Meyer, L. Zhang, and K. Fall, "Report from the IAB [RFC4033] R. Arends, R. Austein, M. Larson, D. Massey, and
Workshop on Routing and Addressing", RFC 4984, S. Rose, "DNS Security Introduction and
September 2007. Requirements", RFC 4033, March 2005.
[RFC5887] B. Carpenter, R. Atkinson, and H. Flinck, [RFC4107] S. Bellovin and R. Housley, "Guidelines for
"Renumbering Still Needs Work", RFC 5887, May 2010. Cryptographic Key Management", RFC 4107, June 2005.
[RFC6115] T. Li, Ed., "Recommendation for a Routing [RFC4116] J. Abley, K. Lindqvist, E. Davies, B. Black, and
Architecture", RFC 6115, February 2011. V. Gill, "IPv4 Multihoming Practices and
Limitations", RFC 4116, July 2005.
Perhaps the most ill-named RFC of all time; it [RFC4786] J. Abley and K. Lindqvist, "Operation of Anycast
contains nothing that could truly be called a Services", RFC 4786, December 2006.
'routing architecture'.
[LISP0] D. Farinacci, V. Fuller, and D. Oran, "Locator/ID [RFC4984] D. Meyer, L. Zhang, and K. Fall, "Report from the
Separation Protocol (LISP)", draft-farinacci-lisp-00 IAB Workshop on Routing and Addressing", RFC 4984,
(work in progress), January 2007. September 2007.
[ALT] V. Fuller, D. Farinacci, D. Meyer, and D. Lewis, [RFC5110] P. Savola, "Overview of the Internet Multicast
"Locator/ID Separation Protocol Alternative Logical Routing Architecture", RFC 5110, January 2008.
Topology (LISP+ALT)", RFC 6836, January 2013.
[NSAP] International Organization for Standardization, [RFC5887] B. Carpenter, R. Atkinson, and H. Flinck,
"Information Processing Systems - Open Systems "Renumbering Still Needs Work", RFC 5887, May 2010.
Interconnection - Basic Reference Model", ISO
Standard 7489.1984, 1984.
[Atkinson] R. Atkinson, "Revised draft proposed definitions", [RFC6115] T. Li, Ed., "Recommendation for a Routing
RRG list message, Message-Id: 808E6500-97B4-4107- Architecture", RFC 6115, February 2011.
8A2F-36BC913BE196@extremenetworks.com, 11 June 2007,
<http://www.ietf.org/mail-archive/web/ram/current/
msg01470.html>.
[Baran] P. Baran, "On Distributed Communications Networks", (Perhaps the most ill-named RFC of all time; it
IEEE Transactions on Communications Systems Vol. contains nothing that could truly be called a
CS-12 No. 1, pp. 1-9, March 1964. 'routing architecture'.)
[Chiappa] J. N. Chiappa, "Endpoints and Endpoint Names: A [ALT] V. Fuller, D. Farinacci, D. Meyer, and D. Lewis,
Proposed Enhancement to the Internet Architecture", "Locator/ID Separation Protocol Alternative Logical
Personal draft (work in progress), 1999, Topology (LISP+ALT)", RFC 6836, January 2013.
<http://www.chiappa.net/~jnc/tech/endpoints.txt>.
[Clark] D. D. Clark, "The Design Philosophy of the DARPA [LISP0] D. Farinacci, V. Fuller, and D. Oran, "Locator/ID
Internet Protocols", in 'Proceedings of the Symposium Separation Protocol (LISP)", draft-farinacci-lisp-00
on Communications Architectures and Protocols SIGCOMM (work in progress), January 2007.
'88', pp. 106-114, 1988.
[Heart] F. E. Heart, R. E. Kahn, S. M. Ornstein, [Future] J. N. Chiappa, "Potential Long-Term Developments
W. R. Crowther, and D. C. Walden, "The Interface With the LISP System",
Message Processor for the ARPA Computer Network", draft-chiappa-lisp-evolution-00 (work in progress),
Proceedings AFIPS 1970 SJCC, Vol. 36, pp. 551-567. October 2012.
[Bibliography] J. N. Chiappa (editor), "LISP (Location/Identity [Baran] P. Baran, "On Distributed Communications Networks",
Separation Protocol) Bibliography", Personal IEEE Transactions on Communications Systems Vol.
site (work in progress), July 2013, <http:// CS-12 No. 1, pp. 1-9, March 1964.
www.chiappa.net/~jnc/tech/lisp/LISPbiblio.html>.
[Iannone] L. Iannone and O. Bonaventure, "On the Cost of [Chiappa] J. N. Chiappa, "Endpoints and Endpoint Names: A
Caching Locator/ID Mappings", in 'Proceedings of the Proposed Enhancement to the Internet Architecture",
3rd International Conference on emerging Networking Personal draft (work in progress), 1999,
EXperiments and Technologies (CoNEXT'07)', ACM, pp. <http://www.chiappa.net/~jnc/tech/endpoints.txt>.
1-12, December 2007.
[Kim] J. Kim, L. Iannone, and A. Feldmann, "A Deep Dive [Clark] D. D. Clark, "The Design Philosophy of the DARPA
Into the LISP Cache and What ISPs Should Know About Internet Protocols", in 'Proceedings of the
It", in 'Proceedings of the 10th International IFIP Symposium on Communications Architectures and
TC 6 Conference on Networking - Volume Part I Protocols SIGCOMM '88', pp. 106-114, 1988.
(NETWORKING '11)', IFIP, pp. 367-378, May 2011.
[CorasCache] F. Coras, A. Cabellos-Aparicio, and J. Domingo- [Saltzer] J. H. Saltzer, D. P. Reed, and D. D. Clark, "End-To-
Pascual, "An Analytical Model for the LISP Cache End Arguments in System Design", ACM TOCS, Vol 2,
Size", in 'Proceedings of the 11th International IFIP No. 4, pp 277-288, November 1984.
TC 6 Networking Conference: Part I', IFIP, pp. 409-
420, May 2012.
[Jakab] L. Jakab, A. Cabellos-Aparicio, F. Coras, D. Saucez, [Heart] F. E. Heart, R. E. Kahn, S. M. Ornstein,
and O. Bonaventure, "LISP-TREE: A DNS Hierarchy to W. R. Crowther, and D. C. Walden, "The Interface
Support the LISP Mapping System", in 'IEEE Journal on Message Processor for the ARPA Computer Network",
Selected Areas in Communications', Vol. 28, No. 8, Proceedings AFIPS 1970 SJCC, Vol. 36, pp. 551-567.
pp. 1332-1343, October 2010.
[Saucez] D. Saucez, L. Iannone, and B. Donnet, "A First [Iannone] L. Iannone and O. Bonaventure, "On the Cost of
Measurement Look at the Deployment and Evolution of Caching Locator/ID Mappings", in 'Proceedings of the
the Locator/ID Separation Protocol", in 'ACM SIGCOMM 3rd International Conference on emerging Networking
Computer Communication Review', Vol. 43 No. 2, pp. EXperiments and Technologies (CoNEXT'07)', ACM, pp.
37-43, April 2013. 1-12, December 2007.
[CorasBGP] F. Coras, D. Saucez, L. Jakab, A. Cabellos-Aparicio, [Kim] J. Kim, L. Iannone, and A. Feldmann, "A Deep Dive
and J. Domingo-Pascual, "Implementing a BGP-free ISP Into the LISP Cache and What ISPs Should Know About
Core with LISP", in 'Proceedings of the Global It", in 'Proceedings of the 10th International IFIP
Communications Conference (GlobeCom)', IEEE, pp. TC 6 Conference on Networking - Volume Part I
2772-2778, December 2012. (NETWORKING '11)', IFIP, pp. 367-378, May 2011.
[Saltzer] J. H. Saltzer, D. P. Reed, and D. D. Clark, "End-To- [CorasCache] F. Coras, A. Cabellos-Aparicio, and J. Domingo-
End Arguments in System Design", ACM TOCS, Vol 2, No. Pascual, "An Analytical Model for the LISP Cache
4, pp 277-288, November 1984. Size", in 'Proceedings of the 11th International
IFIP TC 6 Networking Conference: Part I', IFIP, pp.
409-420, May 2012.
[Jakab] L. Jakab, A. Cabellos-Aparicio, F. Coras, D. Saucez,
and O. Bonaventure, "LISP-TREE: A DNS Hierarchy to
Support the LISP Mapping System", in 'IEEE Journal
on Selected Areas in Communications', Vol. 28, No.
8, pp. 1332-1343, October 2010.
[Saucez] D. Saucez, L. Iannone, and B. Donnet, "A First
Measurement Look at the Deployment and Evolution of
the Locator/ID Separation Protocol", in 'ACM SIGCOMM
Computer Communication Review', Vol. 43 No. 2, pp.
37-43, April 2013.
[CorasBGP] F. Coras, D. Saucez, L. Jakab, A. Cabellos-Aparicio,
and J. Domingo-Pascual, "Implementing a BGP-free ISP
Core with LISP", in 'Proceedings of the Global
Communications Conference (GlobeCom)', IEEE, pp.
2772-2778, December 2012.
[Atkinson] R. Atkinson, "Revised draft proposed definitions",
RRG list message, Message-Id: 808E6500-97B4-4107-
8A2F-36BC913BE196@extremenetworks.com, 11 June 2007,
<http://www.ietf.org/mail-archive/web/ram/current/
msg01470.html>.
[Bibliography] J. N. Chiappa (editor), "LISP (Location/Identity
Separation Protocol) Bibliography", Personal
site (work in progress), July 2013, <http://
www.chiappa.net/~jnc/tech/lisp/LISPbiblio.html>.
Appendix A. Glossary/Definition of Terms Appendix A. Glossary/Definition of Terms
- Address For those who are unfamiliar with the scholarly notation 'q.v.', it
- Locator stands for 'quod vide', which is Latin for 'which see' (literally);
- EID in other words, that term also is defined here.
- RLOC
- ITR - Name: In this document, and in much of computer science, a 'name'
- ETR simply refers to an identifier for an object or entity. Names
- xTR have both semantics (meaning) and syntax (form).[RFC1498]
- PITR - Namespace: A group of names (q.v.) with matching semantics and
- PETR syntax; they usually, but not always, refer to members of a class
- MR of identical objects.
- MS - Node: The general term used to describe any sort of communicating
- DFZ entity; it might be a physical or a virtual host, or a mobile
device of some sort. It was deliberately chosen for use in this
document precisely because its definition is not fixed, and
therefore unlikely to cause erroneous images in the minds of
readers. You will not go far wrong if you think of a node as
being something like a host.
- Switch: A packet switch, in the general meaning of that term.
- Endpoint, end-end communication entity: the fate-sharing region at
one end of an end-end communication; the collection of state
related to both the reliable end-end communication channel, and
the applications running there.
- IPvN: IPv4 or IPv6; the two are so similar, in fundamental
architecture, that in much discussion about their capabilities,
limitations, etc statements about the apply equally to both, and
to continually say "IPv4 and IPv6" quickly becomes tedious.
- Address: In this document, and in current IPvN and similar
networking suites, a 'name' (q.v.) which has mixed semantics, in
that it includes both identity ('who') and location ('where')
semantics.
- Identifier: Here, and in current networking discussions, a 'name'
(q.v.) which has purely identity semantics.
- Locator: Originally defined as a 'name' with location semantics
only, and one that was not necessarily carried in every packet (as
was assumed of 'addresses') [RFC1992], it is now generally taken,
including here, to mean a 'name' with purely location semantics.
- EID, Enpoint Identifier: Originally defined as a name for an
'endpoint' (see the reference), one with purely identity
semantics, and globally unique, and with syntax of relatively
short fixed length [Chiappa]. It is used in the LISP work to mean
the 'identifier' (q.v.) of a node; it is the input to an EID->RLOC
lookup in the 'mapping system' (q.v.); it is usually an IPvN
address. The source and adestination addresses of the innermost
header in a LISP packet are usually EIDs.
- RLOC, Routing Locator: a LISP-specific term meaning the locator of
an entity identified by an EID; as such, it is often the output of
an EID->RLOC lookup in the 'mapping system' (q.v.); it is usually
an IPvN address, and of an ETR. The source and adestination
addresses of the outermost header in a LISP packet are usually
RLOCs.
- ITR, Ingress Tunnel Router: a LISP node at the border of a LISP
site (q.v.) which takes user packets sent to it from inside the
LISP site, encapsulates in a LISP header, and then sends them
across the Internet to an ETR (q.v.); in other words, the start of
a 'tunnel' from the ITR to an ETR.
- ETR: Egress Tunnel Router: a LISP node at the border of a LISP
site (q.v.) which decapsulates user packets which arrive at it
encapsulated in a LISP header, and sends them on towards their
ultimate destination; in other words, the end of the 'tunnel' from
an ITR (q.v.) to the ETR.
- Neighbour ETR: Although an ITR and ETR may be separated by many
actual physical hops, _at the LISP level_, they are direct
neighbours; so any ETR which an ITR sends traffic to is a
'neighbour ETR' of that ITR.
- xTR: An xTR refers to a device which functions both as an ITR and
an ETR (which is typical), when the discussion involves packet
flows in both directions through the device, which results in it
alternately functioning as an ITR and then as an ETR.
- Site: a collection of hosts, routers and networks under a single
administrative control.
- LISP site: A single node, or a set of network elements in an edge
network under the administrative control of a single organization;
they are delimited from the rest of the network by LISP devices
(either separate ITRs and ETRs, or xTRs).
- Reachability, Neighbour ETR Reachability: The ability of an ITR to
be able to send packets to a neighbour ETR (q.v.), or the property
of an ITR to be able to send such packets.
- MR: Map Resolver; a LISP device to which ITRs send requests for
mappings. See Section 6.2.2, "Interface to the Mapping System",
for more.
- MS: Map Server; a LISP device with which ETRs register mappings,
to indicate their availability to handle incoming traffic to the
EIDs covered in those mappings. See Section 6.2.2, "Interface to
the Mapping System" for more.
- Mapping system: the entire ensemble of data and mechanisms which
allow clients - usually ITRs - to find mapppings (from EIDs to
RLOCs). It includes both the mapping database (q.v), and also
everything used to gain access to it - the MRs, the indexing sub-
system (q.v.), etc. See Section 6.2.1, "Mapping System
Organization" for more.
- Mapping database: the term "mapping database" refers to the entire
collection of {EID->RLOC} mappings spread throughout the LISP
system. It is a subset of the 'mapping system' (q.v.). See
Section 6.2, "The Mapping System", for more.
- Indexing sub-system: the entire ensemble of data and mechanisms
which allows MRs to find out which ETR(s) hold the mappping for a
given EID or EID block. It includes both the data on namespace
delegations, as well as the devices which hold that data, and the
protocols used to interact with those devices. See Section 6.2.1,
"Mapping System Organization" for more.
- DDT node: a node in the (abstract) namespace delegation hierarchy.
- DDT server: an actual machine, which one can send packets to, in
the DDT hierarchy - which is, hopefully, a one-to-one projection
of address delegation hierarchy (although of course a single DDT
node may turn into several sibling servers).
- PITR: Proxy ITR; an ITR which is used for interworking between a
LISP-speaking node or site, and legacy nodes or sites; in general,
it acts like a normal ITR, but does so on behalf of LISP devices
which are receiving packets to a legacy device. See
Section 12.2.1.1, "PITRs", for more.
- PETR: Proxy ETR; an ETR which is used for interworking between a
LISP-speaking node or site, and legacy nodes or sites; in general,
it acts like a normal ETR, but does so on behalf of LISP devices
which are sending packets to a legacy device. See
Section 12.2.1.2, "PETRs" for more.
- RTR: Re-encapsulating Tunnel Router; a data plane 'anchor point'
used by a LISP-speaking device to perform functions that can only
be be performed in the core of the network. One use is for LISP-
speaking device behind a NAT device to send and receive traffic
through the NAT device; see [Improvements], Section "Improved NAT
Support" for more.
- DFZ, Default Free Zone: That part of the Internet in which there
are no 'default' entries in routing tables, but where the routing
tables hold entries for every single reachable destination in the
Internet.
Appendix B. Other Appendices Appendix B. Other Appendices
B.1. Old LISP 'Models' B.1. A Brief History of Location/Identity Separation
It was only gradually realized in the networking community that
networks (especially large networks) should deal quite separately
with the identity and location of a node; the distinction between the
two was more than a little hazy at first.
The ARPANET had no real acknowledgment of the difference between the
two. [Heart] [NIC8246] The early Internet also co-mingled the two
([RFC791]), although there was recognition in the early Internet work
that there were two different things going on. [IEN19]
This likely resulted not just from lack of insight, but also the fact
that extra mechanism is needed to support this separation (and in the
early days there were no resources to spare), as well as the lack of
need for it in the smaller networks of the time. (It is a truism of
system design that small systems can get away with doing two things
with one mechanism, in a way that usually will not work when the
system gets much larger.)
The ISO protocol architecture took steps in this direction [NSAP],
but to the Internet community the necessity of a clear separation was
definitively shown by Saltzer. [RFC1498] Later work expanded on
Saltzer's, and tied his separation concepts into the fate-sharing
concepts of Clark. [Clark], [Chiappa]
The separation of location and identity is a step which has recently
been identified by the IRTF as a critically necessary evolutionary
architectural step for the Internet. [RFC6115] However, it has taken
quite some time for this requirement to be generally accepted by the
Internet engineering community at large, although it seems that this
may finally be happening.
Unfortunately, although the development of IPv6 presented a golden
opportunity to learn from this particular failing of IPv4, that
design failed to recognize the need for separation of location and
identity.
B.2. A Brief History of the LISP Project
The LISP system for separation of location and identity resulted from
the discussions of this topic at the Amsterdam IAB Routing and
Addressing Workshop, which took place in October 2006. [RFC4984]
A small group of like-minded personnel from various scattered
locations within Cisco, spontaneously formed immediately after that
workshop, to work on an idea that came out of informal discussions at
the workshop. The first Internet-Draft on LISP appeared in January,
2007, along with a LISP mailing list at the IETF. [LISP0]
Trial implementations started at that time, with initial trial
deployments underway since June 2007; the results of early experience
have been fed back into the design in a continuous, ongoing process
over several years. LISP at this point represents a moderately
mature system, having undergone a long organic series of changes and
updates.
LISP transitioned from an IRTF activity to an IETF WG in March 2009,
and after numerous revisions, the basic specifications moved to
becoming RFCs at the start of 2013 (although work to expand and
improve it, and find new uses for it, continues, and undoubtly will
for a long time to come).
B.3. Old LISP 'Models'
LISP, as initilly conceived, had a number of potential operating LISP, as initilly conceived, had a number of potential operating
modes, named 'models'. Although they are now obsolete, one modes, named 'models'. Although they are now obsolete, one
occasionally sees mention of them, so they are briefly described occasionally sees mention of them, so they are briefly described
here. here.
- LISP 1: EIDs all appear in the normal routing and forwarding - LISP 1: EIDs all appear in the normal routing and forwarding
tables of the network (i.e. they are 'routable');this property is tables of the network (i.e. they are 'routable');this property is
used to 'bootstrap' operation, by using this to load EID->RLOC used to 'bootstrap' operation, by using this to load EID->RLOC
mappings. Packets were sent with the EID as the destination in mappings. Packets were sent with the EID as the destination in
skipping to change at line 2222 skipping to change at page 55, line 39
on a separate network. on a separate network.
- LISP 2: EIDs are not routable; EID->RLOC mappings are available - LISP 2: EIDs are not routable; EID->RLOC mappings are available
from the DNS. from the DNS.
- LISP 3: EIDs are not routable; and have to be looked up in in a - LISP 3: EIDs are not routable; and have to be looked up in in a
new EID->RLOC mapping database (in the initial concept, a system new EID->RLOC mapping database (in the initial concept, a system
using Distributed Hash Tables). Two variants were possible: a using Distributed Hash Tables). Two variants were possible: a
'push' system, in which all mappings were distributed to all ITRs, 'push' system, in which all mappings were distributed to all ITRs,
and a 'pull' system in which ITRs load the mappings they need, as and a 'pull' system in which ITRs load the mappings they need, as
needed. needed.
B.2. Possible Other Appendices B.4. The ALT Mapping Indexing Sub-system
-- Location/Identity Separation Brief History LISP initially used an indexing sub-system called ALT. [ALT] ALT re-
-- LISP History purposed a number of existing mechanisms to provide an indexing
system, which allowed an experimental LISP initial deployment to
become operational without having to write a lot of code, ALT was
relatively easily constructed from basically unmodified existing
mechanisms; it used BGP running over virtual tunnels using GRE.
ALT proved to have a number of issues which made it unsuitable for
large-scale use, and it has now been superseded by DDT. A complete
list of these is not possible here, but the issues mostly were of two
kinds: technical issues which would have arisen at large scale, and
practical operational issues which appeared even in the experimental
deployment.
The biggest operational issues was the effort involved in
configuring, and maintain the configuration, of the virtual tunnels
over which ALT ran (including assigning the addresses for the ends,
etc); also, managing the multiple disjoint routing tables required
was difficult and confusing (even for those who were very familiar
with ALT). Debugging faults in ALT was also difficult; and finally,
because of ALT's nature, administrative issues (who pays for what,
who controls what, etc) were problematic.
However, ALT would have had significant technical issues had it been
used at a larger scale.
The most severe (and fundamental) issue was that since all traffic on
the ALT had to transit the 'root' of the ALT tree, those locations
would have become traffic 'hot-spots' in a large scale deployment.
In addition, optimal performance would have required that the ALT
overall topology be restrained to follow the EID namespace
allocation; however, it was not clear that this was feasible. In any
event, even optimal performance was still less than that in
alternatives. The ALT was also very vulnerable to misconfiguration.
See [Jakab] for more about these issues: the basic structure and
operation of DDT is identical to that of TREE, so the conclusions
drawn there about TREE's superiority to ALT apply equally to DDT.
The ALT did have some useful properties which its replacement, DDT,
did not, e.g. the ability to forward data directly to the
destination, over the ALT, when no mapping was available yet for the
destination. However, these were minor, and heavily outweighed by
its problems.
A recent study, [Saucez], measured actual resolution times in the
deployed LISP network during the changeover from ALT to DDT, allowing
direct comparison of the performance of the two systems. The study
took measurements from a variety of locations in the Internet, with
respect to a number of different target EIDs. The results indicate
that the performance was almost identical; there was more variance
with DDT (perhaps due to the effects of caching), but the greatly
improved scalability of DDT as compared to ALT made that effect
acceptable.
B.5. Early NAT Support
The first mechanism used by LISP to support operation through a NAT
device, described here, has now been superseded by the more general
mechanism proposed in [NAT-Traversal]. That mechanism is, however,
based heavily on this mechanism. The initial mechanism had some
serious limitations, which is why that particular form of it has been
dropped.
First, it only worked with some NATs, those which were configurable
to allow inbound packet traffic to reach a configured host. The NAT
had to be configured to know of the ETR.
Second, since NATs share addresses by using ports, it was only
possible to have a single LISP device behind any given NAT device.
That is because LISP expects all incoming data traffic to be on a
specific port, so it was not possible to have multiple ETRs behind a
single NAT (which normally would have only one global IP address to
share). Even looking at the sort host and port would not necessarily
help, because some source ITR could be sending packets to both ETRs,
so packets to either ETR could also have the identical source host/
port. In short, there was no way for a NAT with multiple ETRs behind
it to know which ETR the packet was for.
To support operation behind a NAT, there was a pair of new LISP
control messages, LISP Echo-Request and Echo-Reply, which allowed the
ETR to discover its temporary global address. The Echo-Request was
sent to the configured Map-Server, and it replied with an Echo-Reply
which included the source address from which the Echo Request was
received (i.e. the public global address assigned to the ETR by the
NAT). The ETR could then insert that address in any Map-Reply
control messages which it sent to correspondent ITRs.
Echo-Request and Echo-Reply have been replaced by Info-Request and
Info-Reply in the replacement, [NAT-Traversal], where they perform
very similar functions; the main change is the addition of the {{xxx
- probably the port, etc to allow multiple XTRs behind a NAT}}.
Author's Address Author's Address
J. Noel Chiappa J. Noel Chiappa
Yorktown Museum of Asian Art Yorktown Museum of Asian Art
Yorktown, Virginia Yorktown, Virginia
USA USA
EMail: jnc@mit.edu EMail: jnc@mit.edu
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