Advertising SID Algorithm Information in BGP
draft-peng-idr-segment-routing-te-policy-attr-02
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Liu Yao , Shaofu Peng | ||
| Last updated | 2022-03-03 | ||
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draft-peng-idr-segment-routing-te-policy-attr-02
IDR Y. Liu
Internet-Draft S. Peng
Intended status: Standards Track ZTE
Expires: 4 September 2022 3 March 2022
Advertising SID Algorithm Information in BGP
draft-peng-idr-segment-routing-te-policy-attr-02
Abstract
This document proposes extensions of BGP and defines some new Segment
Types with algorithm information to meet more requirements when
delivering SR Policy via BGP.
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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Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 4 September 2022.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. New Segment Types for SR-MPLS Adjacency with optional
Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Type M: IPv4 Address + Local Interface ID with optional
Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Type N: IPv4 Local and Remote addresses with optional
Algorithm . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. Type O: IPv6 Address + Interface ID for local and remote
pair with optional Algorithm related SID for SR MPLS . . 5
3.4. Type P: IPv6 Local and Remote addresses with optional
Algorithm for SR MPLS . . . . . . . . . . . . . . . . . . 6
4. New Segment Types for SID only, with optional Algorithm . . . 7
4.1. Type L: MPLS SID only, with optional Algorithm . . . . . 7
4.2. Type Q: SRv6 SID only, with optional Algorithm . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Segment Routing (SR) [RFC8402] allows a headend node to steer a
packet flow along any path. [I-D.ietf-spring-segment-routing-policy]
details the concepts of SR Policy and steering into an SR Policy.
These apply equally to the MPLS and IPv6 data plane instantiations of
Segment Routing with their respective representations of segments as
SR-MPLS SID and SRv6 SID as described in [RFC8402].
[I-D.ietf-idr-segment-routing-te-policy] specifies the way to use BGP
to distribute one or more of the candidate paths of an SR Policy to
the headend of that policy. It defines a new BGP address family
(SAFI), i.e., SR Policy SAFI NLRI. In UPDATE messages of that
address family, the NLRI identifies an SR Policy Candidate Path, and
the attributes encode the segment lists and other details of that SR
Policy Candidate Path. 11 Segment Types (from A to K) are defined to
encode SR-MPLS or SRv6 segments.
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As specified in [I-D.ietf-idr-segment-routing-te-policy], the SR
algorithm can be optionally specified for Segment Types C(IPv4 Node
and SID), D(IPv6 Node and SID for SR-MPLS), I(IPv6 Node and SID for
SRv6), J(IPv6 Node, index for remote and local pair, and SID for
SRv6), and K(IPv6 Local/Remote addresses and SID for SRv6). That is,
currently the algorithm can be carried along with SR-MPLS prefix SID,
SRv6 prefix SID and SRv6 adjacency SID when delivering SR Policy via
BGP.
This document proposes extensions of BGP and defines some new Segment
Types with algorithm information to meet more requirements when
delivering SR Policy via BGP.
2. 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 [RFC2119].
3. New Segment Types for SR-MPLS Adjacency with optional Algorithm
[I-D.ietf-lsr-algorithm-related-adjacency-sid] complements that
besides Prefix-SID, the algorithm can be also included as part of an
Adjacency-SID advertisement for SR-MPLS, in scenarios where multiple
algorithm share the same link resource. In this case, an SR-MPLS
Policy advertised to the headend may also contain algorithm specific
Adjacency-SID.
This section defines 4 new Segment Sub-TLVs of Segment List Sub-TLV
to provide algorithm information for SR-MPLS Adjacency-SID.
The processing procedures for SID with algorithm specified in
[I-D.ietf-spring-segment-routing-policy] and
[I-D.ietf-idr-segment-routing-te-policy] are still applicable for the
new segment types. When the algorithm is not specified for the SID
types above which optionally allow for it, the headend SHOULD use the
Strict Shortest Path algorithm if available; otherwise, it SHOULD use
the default Shortest Path algorithm.
3.1. Type M: IPv4 Address + Local Interface ID with optional Algorithm
The Type M Segment Sub-TLV is similar with existed Type E Segment
Sub-TLV, it also encodes an IPv4 node address, a local interface
Identifier (Local Interface ID) and an optional SR-MPLS SID, but with
additional algorithm information. The format is as follows:
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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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD1
SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402] when A-Flag as defined in section 2.4.4.2.12
[I-D.ietf-idr-segment-routing-te-policy] is present. SR Algorithm is
used by SRPM as described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST be
ignored on receipt.
Other fields have the same meaning as the existing Type E Segment
Sub-TLV.
3.2. Type N: IPv4 Local and Remote addresses with optional Algorithm
The Type N Segment Sub-TLV is similar with existed Type F Segment
Sub-TLV, it also encodes an adjacency local address, an adjacency
remote address and an optional SR-MPLS SID, but with additional
algorithm information. The format is as follows:
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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
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Type: TBD2
SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402] when A-Flag as defined in section 2.4.4.2.12
[I-D.ietf-idr-segment-routing-te-policy] is present. SR Algorithm is
used by SRPM as described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST be
ignored on receipt.
Other fields have the same meaning as existed Type F Segment Sub-TLV.
3.3. Type O: IPv6 Address + Interface ID for local and remote pair with
optional Algorithm related SID for SR MPLS
The Type O Segment Sub-TLV is similar with existed Type G Segment
Sub-TLV, it also encodes an IPv6 Link Local adjacency with IPv6 local
node address, a local interface identifier (Local Interface ID), IPv6
remote node address , a remote interface identifier (Remote Interface
ID) and an optional SR-MPLS SID, but with additional algorithm
information. The format is as follows:
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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Local Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Remote Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD3
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SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402] when A-Flag as defined in section 2.4.4.2.12
[I-D.ietf-idr-segment-routing-te-policy] is present. SR Algorithm is
used by SRPM as described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST be
ignored on receipt.
Other fields have the same meaning as existed Type G Segment Sub-TLV.
3.4. Type P: IPv6 Local and Remote addresses with optional Algorithm
for SR MPLS
The Type P Segment Sub-TLV is similar with existed Type H Segment
Sub-TLV, it also encodes an adjacency local address, an adjacency
remote address and an optional SR-MPLS SID, but with additional
algorithm information. The format is as follows:
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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD4
SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402] when A-Flag as defined in section 2.4.4.2.12
[I-D.ietf-idr-segment-routing-te-policy] is present. SR Algorithm is
used by SRPM as described in section 4 in
[I-D.ietf-spring-segment-routing-policy]. When A-Flag is not
encoded, this field SHOULD be set to zero on transmission and MUST be
ignored on receipt.
Other fields have the same meaning as existed Type H Segment Sub-TLV.
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4. New Segment Types for SID only, with optional Algorithm
Segment Sub-TLV for Type A defined in section 2.4.4.2.1
[I-D.ietf-idr-segment-routing-te-policy] carries only the SID
information in the form of MPLS Label. Segment Sub-TLV for Type B
defined in section 2.4.4.2.2 [I-D.ietf-idr-segment-routing-te-policy]
carries only the SID information in the form of IPv6 address.
If the algorithm information is carried along with the SIDs, it's
useful in the scenarios below:
Scenario 1: The algorithm may be optionally provided to the headend
for verification purposes. The headend can check if the SID value
and the related algorithm received can be found in its SR-DB if
requested to do so.
Scenario 2: The headend may not know about the SID-related algorithm
especially in the inter-domain scenario. Providing the algorithm
information benefits troubleshooting and network management.
This section defines 2 new Segment Sub-TLVs of Segment List Sub-TLV
to provide algorithm information for SR-MPLS/SRv6 SID.
4.1. Type L: MPLS SID only, with optional Algorithm
The Type L Segment Sub-TLV is similar with the Type A Segment Sub-
TLV, it also encodes a single SR-MPLS SID, but with additional
algorithm information. The format is as follows:
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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD5
SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402] when A-Flag as defined in section 2.4.4.2.12
[I-D.ietf-idr-segment-routing-te-policy] is present. When A-Flag is
not encoded, this field SHOULD be set to zero on transmission and
MUST be ignored on receipt.
Other fields have the same meaning as Type A Segment Sub-TLV.
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4.2. Type Q: SRv6 SID only, with optional Algorithm
The Type Q Segment Sub-TLV is similar with existed Type B Segment
Sub-TLV, it also encodes a single SRv6 SID, but with additional
algorithm, endpoint behavior and SID strucutre information. The
format is as follows:
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 | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure (optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type: TBD6
Length is variable.
SR Algorithm: 1 octet specifying SR Algorithm as described in section
3.1.1 in [RFC8402] when A-Flag as defined in section 2.4.4.2.12
[I-D.ietf-idr-segment-routing-te-policy] is present. When A-Flag is
not encoded, this field SHOULD be set to zero on transmission and
MUST be ignored on receipt.
Other fields have the same meaning as the Type B Segment Sub-TLV.
5. IANA Considerations
This document requests codepoint allocations for new Segment Sub-TLVs
in the "SR Policy List Sub-TLVs" registry.
Value Description Reference
------------------------------------------------------------------------
TBD1 Type L MPLS Algorithm related SID sub-TLV This document
TBD2 Type M IPv4 Node, index and Algorithm related This document
SID sub-TLV
TBD3 Type N IPv4 Local/Remote addresses and Algorithm This document
related SID sub-TLV
TBD4 Type O IPv6 Node, index for remote and local pair This document
and Algorithm related SID for SR-MPLS sub-TLV
TBD5 Type P IPv6 Local/Remote addresses and Algorithm This document
related SID sub-TLV
TBD6 Type Q SRv6 Algorithm related SID sub-TLV This document
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6. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security considerations discussed in
[I-D.ietf-idr-segment-routing-te-policy].
7. References
7.1. Normative References
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Jain, D., and S. Lin, "Advertising Segment Routing
Policies in BGP", Work in Progress, Internet-Draft, draft-
ietf-idr-segment-routing-te-policy-14, 10 November 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-14>.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", Work in
Progress, Internet-Draft, draft-ietf-spring-segment-
routing-policy-18, 17 February 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-spring-
segment-routing-policy-18>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
7.2. Informative References
[I-D.ietf-lsr-algorithm-related-adjacency-sid]
Peng, S., Chen, R., Talaulikar, K., and P. Psenak,
"Algorithm Related IGP-Adjacency SID Advertisement", Work
in Progress, Internet-Draft, draft-ietf-lsr-algorithm-
related-adjacency-sid-02, 18 January 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
algorithm-related-adjacency-sid-02>.
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", Work in Progress,
Internet-Draft, draft-ietf-lsr-flex-algo-18, 25 October
2021, <https://datatracker.ietf.org/doc/html/draft-ietf-
lsr-flex-algo-18>.
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[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extensions to Support Segment Routing over
IPv6 Dataplane", Work in Progress, Internet-Draft, draft-
ietf-lsr-isis-srv6-extensions-18, 20 October 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
isis-srv6-extensions-18>.
[I-D.ietf-lsr-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", Work in Progress, Internet-
Draft, draft-ietf-lsr-ospfv3-srv6-extensions-03, 19
November 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-lsr-ospfv3-srv6-extensions-03>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[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>.
[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
December 2019, <https://www.rfc-editor.org/info/rfc8666>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
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[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
Authors' Addresses
Yao Liu
ZTE
Nanjing
China
Email: liu.yao71@zte.com.cn
Shaofu Peng
ZTE
Nanjing
China
Email: peng.shaofu@zte.com.cn
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