Network Working Group S. Previdi, Ed.
Internet-Draft L. Ginsberg
Intended status: Standards Track C. Filsfils
Expires: June 16, 2016 Cisco Systems, Inc.
December 14, 2015
Segment Routing IPv6 Prefix-SID
draft-previdi-isis-ipv6-prefix-sid-01
Abstract
This document defines the Segment Routing IPv6 Prefix-SID sub-TLV.
This new sub-TLV allows to specify which of the prefixes advertised
by a node are to be used as Segment Routing Identifiers (SID) for the
IPv6 dataplane.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 16, 2016.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. SRv6 Prefix SID . . . . . . . . . . . . . . . . . . . . . . . 2
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
With Segment Routing (SR)[I-D.ietf-spring-segment-routing], a node
steers a packet through an ordered list of instructions, called
segments. Segments are identified through Segment Identifiers (SIDs)
that are advertised by routing protocols. The IS-IS extensions for
SR information advertisement are defined in
[I-D.ietf-isis-segment-routing-extensions].
Segment Routing can be directly applied to the IPv6 dataplane through
the use of the Segment Routing Header defined in
[I-D.previdi-6man-segment-routing-header].
When applied to the IPv6 dataplane, the SID is represented by an IPv6
address. This document defines a new IS-IS Prefix sub-TLV where
information related to the IPv6 address used as SR-IPv6 SID is
conveyed.
2. SRv6 Prefix SID
When SR is applied to the IPv6 dataplane, Segment Identifiers (SIDs)
are regular IPv6 addresses that are advertised in routing protocols.
When SR is used over IPv6 dataplane, it is desirable to identify
which of the prefixes originated by a node can be used as SIDs
compared to any other prefix that the node advertises. Moreover, and
in order to provide the same functionalities defined in
[I-D.ietf-spring-segment-routing] and
[I-D.ietf-isis-segment-routing-extensions], a new sub-TLV is defined:
the SRv6-Prefix-SID sub-TLV
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A SRv6-Prefix-SID sub-TLV is associated to a IPv6 prefix advertised
by a node and MAY be present in any of the following TLVs:
TLV-236 (IPv6) defined in [RFC5308].
TLV-237 (MT-IPv6) defined in [RFC5120].
The SRv6-Prefix-SID sub-TLV has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Algorithm |
+-+-+-+-+-+-+-+-+
where:
Type: To be assigned by IANA (suggested value 5).
Length: 3 octets.
Flags: 2 octet field of flags. None of them is defined at this
stage.
Algorithm: the router may use various algorithms when calculating
reachability to other nodes or to prefixes attached to these
nodes. Algorithms identifiers are defined in
[I-D.ietf-isis-segment-routing-extensions]. Examples of these
algorithms are metric based Shortest Path First (SPF), various
sorts of Constrained SPF, etc. The algorithm field of the SRv6-
Prefix-SID contains the identifier of the algorithm the router has
used in order to compute the reachability of the IPv6 prefix that
is used as a SID. At origination, the SRv6-Prefix-SID algorithm
field MUST be set to 0 on all SRv6-Prefix-SIDs of prefixes
computed using SPF algorithm (Shortest Path First). On reception
of the SRv6-Prefix-SID sub-TLV, any non-zero algorithm value MUST
match what advertised in the SR-Algorithm sub-TLV (as defined in
[I-D.ietf-isis-segment-routing-extensions]).
A router advertising an IPv6 prefix with the SRv6-Prefix-SID sub-TLV
MUST support the Segment Routing Header (SRH, defined in
[I-D.previdi-6man-segment-routing-header] and its associated
procedures for packets destined to the advertised prefix. The
advertising router MUST also set the H-flag in the SR-Capability sub-
TLV as defined in [I-D.ietf-isis-segment-routing-extensions].
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Within an area (or within the level-2 subdomain), a router receiving
the advertisement of an IPv6 prefix with the SRv6-Prefix-SID sub-TLV
MUST check whether the originator has set the H-flag in its SR-
Capability Sub-TLV prior to validate the SRv6-Prefix-SID sub-TLV.
A router receiving a SRv6-Prefix-SID from a remote node and with an
algorithm value that such remote node has not advertised in the SR-
Capability sub-TLV (as defined in
[I-D.ietf-isis-segment-routing-extensions]) MUST ignore the SRv6-
Prefix-SID sub-TLV.
The SRv6-Prefix-SID sub-TLV defines the prefix (it is associated to)
as an SR-IPv6 Prefix SID. If the prefix is to be used as a Node-SID:
The IPv6 prefix MUST be advertised with the SRv6-Prefix-SID sub-
TLV attached.
The N-flag defined in [I-D.ietf-isis-prefix-attributes] MUST be
set.
3. IANA Considerations
This document makes the following registrations in the "sub-TLVs for
TLV 135,235,236 and 237" registry.
Type: TBD (suggested value 5)
Description: SRv6 Prefix Segment Identifier
TLV 135: no
TLV 235: no
TLV 236: yes
TLV 237: yes
Reference: This document (Section 2)
4. Security Considerations
This document doesn't introduce new security considerations.
5. Acknowledgements
The authors would like to thank Nagendra Kumar for his review of this
document.
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6. References
6.1. Normative References
[I-D.ietf-isis-prefix-attributes]
Ginsberg, L., Decraene, B., Filsfils, C., Litkowski, S.,
Previdi, S., Xu, X., and U. Chunduri, "IS-IS Prefix
Attributes for Extended IP and IPv6 Reachability", draft-
ietf-isis-prefix-attributes-02 (work in progress),
December 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<http://www.rfc-editor.org/info/rfc5120>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<http://www.rfc-editor.org/info/rfc5308>.
6.2. Informative References
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
Extensions for Segment Routing", draft-ietf-isis-segment-
routing-extensions-05 (work in progress), June 2015.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and r. rjs@rob.sh, "Segment Routing Architecture", draft-
ietf-spring-segment-routing-06 (work in progress), October
2015.
[]
Previdi, S., Filsfils, C., Field, B., Leung, I., Linkova,
J., Kosugi, T., Vyncke, E., and D. Lebrun, "IPv6 Segment
Routing Header (SRH)", draft-previdi-6man-segment-routing-
header-08 (work in progress), October 2015.
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Authors' Addresses
Stefano Previdi (editor)
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: sprevidi@cisco.com
Les Ginsberg
Cisco Systems, Inc.
US
Email: ginsberg@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Brussels
BE
Email: cfilsfil@cisco.com
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