draft-ietf-isis-segment-routing-msd-15.txt   draft-ietf-isis-segment-routing-msd-16.txt 
IS-IS Working Group J. Tantsura IS-IS Working Group J. Tantsura
Internet-Draft Nuage Networks Internet-Draft Nuage Networks
Intended status: Standards Track U. Chunduri Intended status: Standards Track U. Chunduri
Expires: March 2, 2019 Huawei Technologies Expires: March 27, 2019 Huawei Technologies
S. Aldrin S. Aldrin
Google, Inc Google, Inc
L. Ginsberg L. Ginsberg
Cisco Systems Cisco Systems
August 29, 2018 September 23, 2018
Signaling MSD (Maximum SID Depth) using IS-IS Signaling MSD (Maximum SID Depth) using IS-IS
draft-ietf-isis-segment-routing-msd-15 draft-ietf-isis-segment-routing-msd-16
Abstract Abstract
This document defines a way for an Intermediate System to This document defines a way for an Intermediate System to
Intermediate System (IS-IS) Router to advertise multiple types of Intermediate System (IS-IS) router to advertise multiple types of
supported Maximum SID Depths (MSDs) at node and/or link granularity. supported Maximum SID Depths (MSDs) at node and/or link granularity.
Such advertisements allow entities (e.g., centralized controllers) to Such advertisements allow entities (e.g., centralized controllers) to
determine whether a particular SID stack can be supported in a given determine whether a particular SID stack can be supported in a given
network. This document only defines one type of MSD maximum label network. This document only defines one type of MSD maximum label
imposition, but defines an encoding that can support other MSD types. imposition, but defines an encoding that can support other MSD types.
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
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 March 2, 2019. This Internet-Draft will expire on March 27, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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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2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 3 2. Node MSD Advertisement . . . . . . . . . . . . . . . . . . . 3
3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4 3. Link MSD Advertisement . . . . . . . . . . . . . . . . . . . 4
4. Procedures for using Node and Link MSD Advertisements . . . . 5 4. Procedures for using Node and Link MSD Advertisements . . . . 5
5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6 5. Base MPLS Imposition MSD . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
When Segment Routing (SR) paths are computed by a centralized When Segment Routing (SR) paths are computed by a centralized
controller, it is critical that the controller learns the Maximum SID controller, it is critical that the controller learns the Maximum SID
Depth (MSD) that can be imposed at each node/link a given SR path to Depth (MSD) that can be imposed at each node/link of a given SR path
insure that the Segment Identifier (SID) stack depth of a computed to insure that the Segment Identifier (SID) stack depth of a computed
path doesn't exceed the number of SIDs the node is capable of path does not exceed the number of SIDs the node is capable of
imposing. imposing.
Path Computation Element Protocol (PCEP) SR extensions draft [I-D.ietf-pce-segment-routing] defines how to signal MSD in the SR
[I-D.ietf-pce-segment-routing] signals MSD in SR Path Computation Path Computation Element (PCE) Capability TLV and in the METRIC
Element (PCE) Capability TLV and METRIC Object. However, if PCEP is Object originally defined in [RFC5440]. However, if PCEP is not
not supported/configured on the head-end of an SR tunnel or a supported/configured on the head-end of an SR tunnel or a Binding-SID
Binding-SID anchor node and controller does not participate in IGP anchor node and controller does not participate in IGP routing, it
routing, it has no way to learn the MSD of nodes and links. BGP-LS has no way to learn the MSD of nodes and links. BGP-LS (Distribution
(Distribution of Link-State and TE Information using Border Gateway of Link-State and TE Information using Border Gateway Protocol)
Protocol) [RFC7752] defines a way to expose topology and associated [RFC7752] defines a way to expose topology and associated attributes
attributes and capabilities of the nodes in that topology to a and capabilities of the nodes in that topology to a centralized
centralized controller. MSD signaling by BGP-LS has been defined in controller. MSD signaling by BGP-LS has been defined in
[I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is [I-D.ietf-idr-bgp-ls-segment-routing-msd]. Typically, BGP-LS is
configured on a small number of nodes that do not necessarily act as configured on a small number of nodes that do not necessarily act as
head-ends. In order for BGP-LS to signal MSD for all the nodes and head-ends. In order for BGP-LS to signal MSD for all the nodes and
links in the network MSD is relevant, MSD capabilities should be links in the network MSD is relevant, MSD capabilities should be
advertised by every Intermediate System to Intermediate System(IS-IS) advertised by every Intermediate System to Intermediate System(IS-IS)
router in the network. router in the network.
Other types of MSD are known to be useful. For example, Other types of MSD are known to be useful. For example,
[I-D.ietf-isis-mpls-elc] defines Readable Label Depth Capability [I-D.ietf-isis-mpls-elc] defines Readable Label Depth Capability
(RLDC) that is used by a head-end to insert an Entropy Label (EL) at (RLDC) that is used by a head-end to insert an Entropy Label (EL) at
a depth, that could be read by transit nodes. a depth, that could be read by transit nodes.
This document defines an extension to IS-IS used to advertise one or This document defines an extension to IS-IS used to advertise one or
more types of MSD at node and/or link granularity. It also creates more types of MSD at node and/or link granularity. It also creates
an IANA registry for assigning MSD type identifiers. It also defines an IANA registry for assigning MSD type identifiers. It also defines
the Base MPLS Imposition MSD type. In the future it is expected, the Base MPLS Imposition MSD type. In the future it is expected that
that new MSD types will be defined to signal additional capabilities new MSD types will be defined to signal additional capabilities e.g.,
e.g., entropy labels, SIDs that can be imposed through recirculation, entropy labels, SIDs that can be imposed through recirculation, or
or SIDs associated with another dataplane e.g., IPv6. Although MSD SIDs associated with another dataplane e.g., IPv6.
advertisements are associated with Segment Routing, the
Although MSD advertisements are associated with Segment Routing, the
advertisements MAY be present even if Segment Routing itself is not advertisements MAY be present even if Segment Routing itself is not
enabled. Note that in a non-SR MPLS network, label depth is what is enabled. Note that in a non-SR MPLS network, label depth is what is
defined by the MSD advertisements. defined by the MSD advertisements.
1.1. Terminology 1.1. Terminology
BMI: Base MPLS Imposition is the number of MPLS labels which can be BMI: Base MPLS Imposition is the number of MPLS labels which can be
imposed inclusive of all service/transport/special labels imposed inclusive of all service/transport/special labels
MSD: Maximum SID Depth - the number of SIDs a node or a link on a MSD: Maximum SID Depth - the number of SIDs supported by a node or a
node can support link on a node
SID: Segment Identifier as defined in [RFC8402]
1.2. Requirements Language 1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here . capitals, as shown here .
2. Node MSD Advertisement 2. Node MSD Advertisement
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If there exist multiple Node MSD advertisements for the same MSD-Type If there exist multiple Node MSD advertisements for the same MSD-Type
originated by the same router, the procedures defined in [RFC7981] originated by the same router, the procedures defined in [RFC7981]
apply. These procedures may result in different MSD values being apply. These procedures may result in different MSD values being
used by (for example) different controllers - but this does not used by (for example) different controllers - but this does not
create any interoperability issue. create any interoperability issue.
3. Link MSD Advertisement 3. Link MSD Advertisement
The link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and The link MSD sub-TLV is defined for TLVs 22, 23, 25, 141, 222, and
223 to carry the MSD of the interface associated with the link. MSD 223 to carry the MSD of the interface associated with the link. MSD
values may be learned via a hardware API or may be provisioned. values may be signaled by the forwarding plane or may be provisioned.
0 1 0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value | | MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ................... // // ................... //
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length of value field. length of value field.
Value: consists of one or more pairs of a 1 octet MSD-Type and 1 Value: consists of one or more pairs of a 1 octet MSD-Type and 1
octet MSD-Value. octet MSD-Value.
MSD-Type is a value defined in the MSD Types registry created by the MSD-Type is a value defined in the MSD Types registry created by the
IANA Section of this document. IANA Section of this document.
MSD-Value is a number in the range of 0-255. For all MSD-Types, 0 MSD-Value is a number in the range of 0-255. For all MSD-Types, 0
represents lack of the ability to support SID stack of any depth; any represents lack of the ability to support SID stack of any depth; any
other value represents that of the link when used as an outgoing other value represents that of the link.
link.
This sub-TLV is optional. This sub-TLV is optional.
If multiple Link MSD advertisements for the same MSD-Type and the If multiple Link MSD advertisements for the same MSD-Type and the
same link are received, the procedure used to select which copy is same link are received, the procedure used to select which copy is
used is undefined. used is undefined.
4. Procedures for using Node and Link MSD Advertisements 4. Procedures for using Node and Link MSD Advertisements
When Link MSD is present for a given MSD type, the value of the Link When Link MSD is present for a given MSD type, the value of the Link
MSD MUST take preference over the Node MSD. When a Link MSD type is MSD MUST take precedence over the Node MSD. When a Link MSD type is
not signaled but the Node MSD type is, then the Node MSD type value not signaled but the Node MSD type is, then the Node MSD type value
MUST be considered as the MSD value for that link. MUST be considered as the MSD value for that link.
In order to increase flooding efficiency, it is RECOMMENDED that In order to increase flooding efficiency, it is RECOMMENDED that
routers with homogenous link MSD values advertise just the Node MSD routers with homogenous link MSD values advertise just the Node MSD
value. value.
The meaning of the absence of both Node and Link MSD advertisements The meaning of the absence of both Node and Link MSD advertisements
for a given MSD type is specific to the MSD type. Generally it can for a given MSD type is specific to the MSD type. Generally it can
only be inferred that the advertising node does not support only be inferred that the advertising node does not support
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y y y y y y y y y y y y
Figure 5: TLVs where LINK MSD Sub-TLV can be present Figure 5: TLVs where LINK MSD Sub-TLV can be present
This document requests creation of an IANA managed registry under the This document requests creation of an IANA managed registry under the
category of "Interior Gateway Protocol (IGP) Parameters" IANA category of "Interior Gateway Protocol (IGP) Parameters" IANA
registries to identify MSD types as proposed in Section 2 and registries to identify MSD types as proposed in Section 2 and
Section 3. The registration procedure is "Expert Review" as defined Section 3. The registration procedure is "Expert Review" as defined
in [RFC8126]. Suggested registry name is "IGP MSD Types". Types are in [RFC8126]. Suggested registry name is "IGP MSD Types". Types are
an unsigned 8 bit number. The following values are defined by this an unsigned 8 bit number. The following values are defined by this
document document:
Value Name Reference Value Name Reference
----- --------------------- ------------- ----- --------------------- -------------
0 Reserved This document 0 Reserved This document
1 Base MPLS Imposition MSD This document 1 Base MPLS Imposition MSD This document
2-250 Unassigned This document 2-250 Unassigned This document
251-254 Experimental This document 251-254 Experimental This document
255 Reserved This document 255 Reserved This document
Figure 6: MSD Types Codepoints Registry Figure 6: MSD Types Codepoints Registry
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General guidance for the Designated Experts is as defined in General guidance for the Designated Experts is as defined in
[RFC7370] [RFC7370]
7. Security Considerations 7. Security Considerations
Security considerations as specified by [RFC7981] are applicable to Security considerations as specified by [RFC7981] are applicable to
this document. this document.
Advertisement of the additional information defined in this document Advertisement of the additional information defined in this document
that is false, e.g., an MSD that is incorrect, may result in a path that is false, e.g., an MSD that is incorrect, may result in a path
computation failing, having a service unavailable, or instantiation computation failing, having a service unavailable, or calculation of
of a path that can't be supported by the head-end (the node a path that cannot be supported by the head-end (the node performing
performing the imposition). the imposition).
The presence of this information also may inform an attacker of how The presence of this information also may inform an attacker of how
to induce any of the aforementioned conditions. to induce any of the aforementioned conditions.
8. Contributors 8. Contributors
The following people contributed to this document: The following people contributed to this document:
Peter Psenak Peter Psenak
Email: ppsenak@cisco.com Email: ppsenak@cisco.com
skipping to change at page 8, line 21 skipping to change at page 8, line 21
10. References 10. References
10.1. Normative References 10.1. 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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints [RFC7370] Ginsberg, L., "Updates to the IS-IS TLV Codepoints
Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014, Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014,
<https://www.rfc-editor.org/info/rfc7370>. <https://www.rfc-editor.org/info/rfc7370>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981, for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016, DOI 10.17487/RFC7981, October 2016,
<https://www.rfc-editor.org/info/rfc7981>. <https://www.rfc-editor.org/info/rfc7981>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-idr-bgp-ls-segment-routing-msd] [I-D.ietf-idr-bgp-ls-segment-routing-msd]
Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan, Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
"Signaling MSD (Maximum SID Depth) using Border Gateway "Signaling MSD (Maximum SID Depth) using Border Gateway
Protocol Link-State", draft-ietf-idr-bgp-ls-segment- Protocol Link-State", draft-ietf-idr-bgp-ls-segment-
routing-msd-02 (work in progress), August 2018. routing-msd-02 (work in progress), August 2018.
[I-D.ietf-isis-mpls-elc] [I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S. Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
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