draft-ietf-savi-mix-00.txt   draft-ietf-savi-mix-01.txt 
Network Working Group J. Bi Network Working Group J. Bi
Internet-Draft CERNET Internet-Draft CERNET
Intended status: Standards Track G. Yao Intended status: Standards Track G. Yao
Expires: November 7, 2011 Tsinghua University Expires: April 28, 2012 Tsinghua University
J. Halpern J. Halpern
Newbridge Networks Inc Newbridge Networks Inc
E. Levy-Abegnoli, Ed. E. Levy-Abegnoli, Ed.
Cisco Systems Cisco Systems
May 6, 2011 October 26, 2011
SAVI for Mixed Address Assignment Methods Scenario SAVI for Mixed Address Assignment Methods Scenario
draft-ietf-savi-mix-00 draft-ietf-savi-mix-01
Abstract Abstract
This document reviews how multiple address discovery methods can This document reviews how multiple address discovery methods can
coexist in a single SAVI device and collisions are resolved when the coexist in a single SAVI device and collisions are resolved when the
same binding entry is discovered by two or more methods. same binding entry is discovered by two or more methods.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 7, 2011. This Internet-Draft will expire on April 28, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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4.2. Same Address on the Same Binding Anchor . . . . . . . . . . 6 4.2. Same Address on the Same Binding Anchor . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . . 6 5.1. Normative References . . . . . . . . . . . . . . . . . . . 6
5.2. Informative References . . . . . . . . . . . . . . . . . . 6 5.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Contributors and Acknowledgments . . . . . . . . . . . 7 Appendix A. Contributors and Acknowledgments . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
There are currently several documents [I-D.ietf-savi-fcfs], There are currently several documents [I-D.ietf-savi-fcfs],
[I-D.ietf-savi-dhcp], [I-D.ietf-savi-send] that describe the [I-D.ietf-savi-dhcp] and [I-D.ietf-savi-send] that describe the
different methods by which a switch can discover and record bindings different methods by which a switch can discover and record bindings
between a node's layer3 address and a binding anchor and use that between a node's layer3 address and a binding anchor and use that
binding to perform Source Address Validation. binding to perform Source Address Validation. Each of these
documents specifies how to learn on-link addresses, based on the
The method used by nodes to assign the address drove the break down method used for their assignment, respectively: StateLess
into these multiple documents, whether StateLess Autoconfiguration Autoconfiguration (SLAAC), Dynamic Host Control Protocol (DHCP) and
(SLAAC), Dynamic Host Control Protocol (DHCP), Secure Neighbor Secure Neighbor Discovery (SeND). Each of these documents describes
Discovery (SeND) or manual. Each of these documents describes
separately how one particular discovery method deals with address separately how one particular discovery method deals with address
collisions (same address, different anchor). collisions (same address, different anchor).
While multiple assignment methods can be used in the same layer2 While multiple assignment methods can be used in the same layer2
domain, a SAVI device might have to deal with a mix of binding domain, a SAVI device might have to deal with a mix of binding
discovery methods. The purpose of this document is to provide discovery methods. The purpose of this document is to provide
recommendations to avoid collisions and to review collisions handling recommendations to avoid collisions and to review collisions handling
when two or more such methods come up with competing bindings. when two or more such methods come up with competing bindings.
2. Problem Scope 2. Problem Scope
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SAVI solution is enabled on a SAVI device, the method is referred to SAVI solution is enabled on a SAVI device, the method is referred to
as "mix address assignment method" in this document. as "mix address assignment method" in this document.
SAVI solutions are independent from each other, each one handling its SAVI solutions are independent from each other, each one handling its
own entries. In the absence of reconciliation, each solution will own entries. In the absence of reconciliation, each solution will
reject packets sourced with an address it did not discovered. To reject packets sourced with an address it did not discovered. To
prevent addresses discovered by one solution to be filtered out by prevent addresses discovered by one solution to be filtered out by
another, the binding table should be shared by all the solutions. another, the binding table should be shared by all the solutions.
However this could create some conflict when the same entry is However this could create some conflict when the same entry is
discovered by two different methods: the purpose of this document is discovered by two different methods: the purpose of this document is
of two folds: provide recommendations to avoid conflicts, and resolve of two folds: provide recommendations and method to avoid conflicts,
conflicts if and when they happen. Collisions happening within a and resolve conflicts if and when they happen. Collisions happening
given solution are outside the scope of this document. within a given solution are outside the scope of this document.
3. Recommendations for preventing collisions 3. Recommendations for preventing collisions
If each solution has a dedicated address space, collisions won't If each solution has a dedicated address space, collisions won't
happen. Thus, in order to avoid overlap in the address space across happen. Using non overlapping address space across SAVI solutions is
SAVI solutions enabled on any particular SAVI device, it is therefore recommended. To that end, one should:
recommended to
1. DHCP/SLAAC: separate the prefix scope of DHCP and SLAAC. Set the 1. DHCP/SLAAC: use non-overlapping prefix for DHCP and SLAAC. Set
A bit in Prefix information option of Router Advertisement for the A bit in Prefix information option of Router Advertisement
SLAAC prefix. And set the M bit in Router Advertisement for DHCP for SLAAC prefix. And set the M bit in Router Advertisement for
prefix. [RFC4861] [RFC4862]. DHCP prefix. For detail explanations on these bits, refer to
[RFC4861] [RFC4862].
2. SeND/non-SeND: avoid mixed environment (where SeND and non-SeND 2. SeND/non-SeND: avoid mixed environment (where SeND and non-SeND
nodes are deployed) or separate the prefixes announced to SeND nodes are deployed) or separate the prefixes announced to SeND
and non-SenD nodes. One way to separate the prefixes is to have and non-SenD nodes. One way to separate the prefixes is to have
the router()s announcing different (non-overlapping) prefixes to the router()s announcing different (non-overlapping) prefixes to
SeND and to non-SeND nodes, using unicast Router Advertisements, SeND and to non-SeND nodes, using unicast Router Advertisements,
in response to SeND/non-SeND Router Solicit. in response to SeND/non-SeND Router Solicit.
4. Handing binding collisions 4. Handing binding collisions
In situations where collisions could not be avoided, two cases should In situations where collisions could not be avoided, two cases should
be considered: be considered:
1. The same address is bound on two different binding anchors by 1. The same address is bound on two different binding anchors by
different SAVI solutions. different SAVI solutions.
2. The same address is bound on the same binding anchor by different 2. The same address is bound on the same binding anchor by different
SAVI solutions. SAVI solutions.
4.1. Same Address on Different Binding Anchors 4.1. Same Address on Different Binding Anchors
This is the very case of collision that could not be prevented by This would typically occur in case assignment address spaces could
separating the assignment address spaces. For instance, an address not be separated. For instance,overl an address is assigned by SLAAC
is assigned by SLAAC on node X, installed in the binding table using on node X, installed in the binding table using SAVI-FCFS, anchored
SAVI-FCFS, anchored to "anchor-X". Later, the same address is to "anchor-X". Later, the same address is assigned by DHCP to node
assigned by DHCP to node Y, as a potential candidate in the same Y, as a potential candidate in the same binding table, anchored to
binding table, anchored to "anchor-Y". "anchor-Y".
4.1.1. Basic preference 4.1.1. Basic preference
Within the SAVI perimeter, one address bound to a binding anchor by The SAVI device must decide whom the address should be bound with
one SAVI solution could also be bound by another SAVI solution to a (anchor-X or anchor-Y in this example). Current standard documents
different binding anchor. If the DAD procedure is not performed, the of address assignment methods have implied the prioritization
same address will also be bound to the new binding anchor. Both relationship (first-come). In the absence of any configuration or
bindings are legitimate within the corresponding solution. protocol hint (see Section 4.1.2) the SAVI device should choose the
first-come entry, whether it was learnt from SLACC, SeND or DHCP.
Though it is possible that the hosts and network can still work in
such scenario, the uniqueness of address is not insured. The SAVI
device must decide whom the address should be bound with. Current
standard documents of address assignment methods have implied the
prioritization relationship (first-come). In the absence of any
configuration or protocol hint (see Section 4.1.2) the SAVI device
should choose the first-come entry, whether it was learnt from SLACC,
SeND or DHCP.
4.1.2. Overwritten preference 4.1.2. Overwritten preference
There are two identified exceptions to the general prioritization There are two identified exceptions to the general prioritization
model, one of them being CGA addresses, another one controlled by the model, one of them being CGA addresses, another one controlled by the
configuration of the switch: configuration of the switch:
1. When CGA addresses are used, and a collision is detected, 1. When CGA addresses are used, and a collision is detected,
preference should be given to the anchor that carries the CGA preference should be given to the anchor that carries the CGA
credentials once they are verified, in particular the CGA credentials once they are verified, in particular the CGA
parameters and the RSA options. parameters and the RSA options. Note that if an attacker was
2. The SAVI device should allow the configuration of a prefix or a trying to replay CGA credentials, he would then compete on the
single address, together with a given anchor or constrained to be base of fcfs (first-come, first-serve).
discovered by a particular SAVI solution (see also "Prefix 2. The SAVI device should allow the configuration of a triplet
Configuration" section in [I-D.ietf-savi-framework]. If a DAD ("prefix", "anchor", "method") or ("address", "anchor",
message for a target within a configured prefix (or equal to a "method"). Later, if a DAD message is received for a target
configured single address) is received on the SAVI device from an within "prefix" (or equal "address") bound to "anchor1"
anchor, or via a discovery method different from the one (different from "anchor"), or via a discovery method different
configured, the switch should defend the address by responding to from "method", the switch should defend the address by responding
the DAD message. It should not at this point install an entry to the DAD message. It should not at this point install the
into the binding table. This is especially useful to protect entry into the binding table. It will simply prevent the node to
well known bindings such as a static address of a server over assign the address, and will de-facto prioritize the configured
anybody, even when the server is down. It is also a way to give anchor or configured assignment method for that address. This is
priority to a binding learnt from SAVI-DHCP over a binding for especially useful to protect well known bindings such as a static
the same address, learnt from SAVI-FCFS. address of a server over anybody, even when the server is down.
It is also a way to give priority to a binding learnt from SAVI-
DHCP over a binding for the same address, learnt from SAVI-FCFS.
4.1.3. Multiple SAVI Device Scenario 4.1.3. Multiple SAVI Device Scenario
A single SAVI device doesn't have the information of all bound A single SAVI device doesn't have the information of all bound
addresses on the perimeter. Therefore it is not enough to lookup addresses on the perimeter. Therefore it is not enough to lookup
local bindings to identify a collision. However, assuming DAD is local bindings to identify a collision. However, assuming DAD is
performed throughout the security perimeter for all addresses performed throughout the security perimeter for all addresses
regardless of the assignment method, then DAD response will inform regardless of the assignment method, then DAD response will inform
all SAVI devices about any collision. In that case, FCFS will apply all SAVI devices about any collision. In that case, FCFS will apply
the same way as in a single switch scenario. If the admin configured the same way as in a single switch scenario. If the admin configured
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5.1. Normative References 5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
5.2. Informative References 5.2. Informative References
[I-D.ietf-savi-dhcp] [I-D.ietf-savi-dhcp]
Wu, J., Yao, G., Bi, J., and F. Baker, "SAVI Solution for Wu, J., Yao, G., Bi, J., and F. Baker, "SAVI Solution for
DHCP", draft-ietf-savi-dhcp-09 (work in progress), DHCP", draft-ietf-savi-dhcp-10 (work in progress),
April 2011. July 2011.
[I-D.ietf-savi-fcfs] [I-D.ietf-savi-fcfs]
Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
SAVI: First-Come First-Serve Source-Address Validation for SAVI: First-Come First-Serve Source-Address Validation for
Locally Assigned IPv6 Addresses", draft-ietf-savi-fcfs-09 Locally Assigned IPv6 Addresses", draft-ietf-savi-fcfs-09
(work in progress), April 2011. (work in progress), April 2011.
[I-D.ietf-savi-framework] [I-D.ietf-savi-framework]
Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt,
"Source Address Validation Improvement Framework", "Source Address Validation Improvement Framework",
draft-ietf-savi-framework-04 (work in progress), draft-ietf-savi-framework-05 (work in progress),
March 2011. July 2011.
[I-D.ietf-savi-send] [I-D.ietf-savi-send]
Bagnulo, M. and A. Garcia-Martinez, "SEND-based Source- Bagnulo, M. and A. Garcia-Martinez, "SEND-based Source-
Address Validation Implementation", Address Validation Implementation",
draft-ietf-savi-send-05 (work in progress), April 2011. draft-ietf-savi-send-06 (work in progress), October 2011.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998. (IPv6) Specification", RFC 2460, December 1998.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003. IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005. Neighbor Discovery (SEND)", RFC 3971, March 2005.
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