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LSR                                                            P. Shaofu
Internet-Draft                                                    C. Ran
Intended status: Standards Track                         ZTE Corporation
Expires: March 29, 2021                               September 25, 2020


           Algorithm Related IGP-Adjacency SID Advertisement
           draft-peng-lsr-algorithm-related-adjacency-sid-01

Abstract

   Segment Routing architecture supports the use of multiple routing
   algorithms, i.e, different constraint-based shortest-path
   calculations can be supported.  There are two standard algorithms:
   SPF and Strict-SPF, defined in Segment Routing architecture.  There
   are also other user defined algorithms according to Flex-algo
   applicaiton.  However, an algorithm identifier is often included as
   part of a Prefix-SID advertisement, that maybe not satisfy some
   scenarios where multiple algorithm share the same link resource.
   This document complement that the algorithm identifier can be also
   included as part of a Adjacency-SID advertisement

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 29, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Adjacency Segment Identifier per Algorithm  . . . . . . . . .   3
     3.1.  ISIS Adjacency Segment Identifier per Algorithm . . . . .   3
       3.1.1.  ISIS Adjacency Segment Identifier (Adj-SID) per
               Algorithm Sub-TLV . . . . . . . . . . . . . . . . . .   4
       3.1.2.  ISIS Adjacency Segment Identifier (LAN-Adj-SID) per
               Algorithm Sub-TLV . . . . . . . . . . . . . . . . . .   4
     3.2.  OSPF Adjacency Segment Identifier per Algorithm . . . . .   5
       3.2.1.  OSPF Adj-SID Sub-TLV  . . . . . . . . . . . . . . . .   6
       3.2.2.  OSPF LAN Adj-SID Sub-TLV  . . . . . . . . . . . . . .   6
     3.3.  OSPFv3 Adjacency Segment Identifier per Algorithm . . . .   7
       3.3.1.  OSPFv3 Adj-SID Sub-TLV  . . . . . . . . . . . . . . .   7
       3.3.2.  OSPFv3 LAN Adj-SID Sub-TLV  . . . . . . . . . . . . .   8
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Segment Routing architecture [RFC8402] supports the use of multiple
   routing algorithms, i.e, different constraint-based shortest-path
   calculations can be supported.  There are two standard algorithms,
   i.e, SPF and Strict-SPF, that defined in Segment Routing
   architecture.  For SPF, the packet is forwarded along the well known
   ECMP-aware Shortest Path First (SPF) algorithm employed by the IGPs.
   However, it is explicitly allowed for a midpoint to implement another
   forwarding based on local policy.  For Strict Shortest Path First
   (Strict-SPF), it mandates that the packet be forwarded according to
   the ECMP-aware SPF algorithm and instructs any router in the path to
   ignore any possible local policy overriding the SPF decision.

   There are also other user defined algorithms according to IGP Flex
   Algorithm [I-D.ietf-lsr-flex-algo].  IGP Flex Algorithm proposes a
   solution that allows IGPs themselves to compute constraint based
   paths over the network, and it also specifies a way of using Segment
   Routing (SR) Prefix-SIDs and SRv6 locators to steer packets along the



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   constraint-based paths.  It specifies a set of extensions to ISIS,
   OSPFv2 and OSPFv3 that enable a router to send TLVs that identify (a)
   calculation-type, (b) specify a metric-type, and (c )describe a set
   of constraints on the topology, that are to be used to compute the
   best paths along the constrained topology.  A given combination of
   calculation-type, metric-type, and constraints is known as an FAD
   (Flexible Algorithm Definition).

   However, an algorithm identifier is often included as part of a
   Prefix-SID advertisement, that maybe not satisfy some scenarios where
   multiple algorithm share the same link resource.  For example, an SR-
   TE policy may be instantiated within specific Flex-algo plane, i.e.,
   the SID list requires to include algorithm related SIDs.  An
   algorithm-unware Adjacency-SID included in the SID list can just
   steer the packet towards the link, but can not apply different QoS
   policy for different algorithm.  Another example is that the TI-LFA
   backup path computed in Flex-algo plane may also contain an
   algorithm-unware Adjacency-SID, which maybe also used in other SR-TE
   instance that carries other service.

   This document complement that the algorithm identifier can be also
   included as part of an Adjacency-SID advertisement for SR-MPLS.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Adjacency Segment Identifier per Algorithm

3.1.  ISIS Adjacency Segment Identifier per Algorithm

   [RFC8667] describes the IS-IS extensions that need to be introduced
   for Segment Routing operating on an MPLS data plane.  It defined
   Adjacency Segment Identifier (Adj-SID) sub-TLV advertised with TLV-
   22/222/23/223/141, and Adjacency Segment Identifier (LAN-Adj-SID)
   Sub-TLV advetised with TLV-22/222/23/223.  Accordingly, this document
   defines two new optional Sub-TLVs, "ISIS Adjacency Segment Identifier
   (Adj-SID) per Algorithm Sub-TLV" and "ISIS Adjacency Segment
   Identifier (LAN-Adj-SID) per Algorithm Sub-TLV".








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3.1.1.  ISIS Adjacency Segment Identifier (Adj-SID) per Algorithm Sub-
        TLV

   ISIS Adjacency Segment Identifier (Adj-SID) per Algorithm 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     |     Weight    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Algorithm   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         SID/Label/Index (variable)            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Figure 1: ISIS Adjacency Segment Identifier (Adj-SID) per Algorithm
                                  Format

   where:

   Type: TBD1.

   Length: 6 or 7 depending on size of the SID.

   Flags: Refer to Adjacency Segment Identifier (Adj-SID) sub-TLV.

   Weight: Refer to Adjacency Segment Identifier (Adj-SID) sub-TLV.

   Algorithm: The Algorithm field contains the identifier of the
   algorithm the router uses to apply algorithm specific QoS policy
   configured on the adjacency.

   SID/Label/Index: Refer to Adjacency Segment Identifier (Adj-SID) sub-
   TLV.

   For a P2P link, an SR-capable router MAY allocate different Adj-SID
   for different algorithm, if this link will join different algorithm
   related plane.

3.1.2.  ISIS Adjacency Segment Identifier (LAN-Adj-SID) per Algorithm
        Sub-TLV

   ISIS Adjacency Segment Identifier (LAN-Adj-SID) per Algorithm Sub-TLV
   has the following format:





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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    |    Weight     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Algorithm   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  Neighbor System-ID (ID length octets)        |
      +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   SID/Label/Index (variable)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


       Figure 2: ISIS Adjacency Segment Identifier (LAN-Adj-SID) per
                             Algorithm Format

   where:

   Type: TBD2.

   Length: Variable.

   Flags: Refer to Adjacency Segment Identifier (LAN-Adj-SID) Sub-TLV.

   Weight: Refer to Adjacency Segment Identifier (LAN-Adj-SID) Sub-TLV.

   Algorithm: The Algorithm field contains the identifier of the
   algorithm the router uses to apply algorithm specific QoS policy
   configured on the adjacency.

   SID/Label/Index: Refer to Adjacency Segment Identifier (LAN-Adj-SID)
   Sub-TLV.

   For a broadcast link, an SR-capable router MAY allocate different
   Adj-SID for different algorithm, if this link will join different
   algorithm related plane.

3.2.  OSPF Adjacency Segment Identifier per Algorithm

   [RFC8665] describes the OSPF extensions that need to be introduced
   for Segment Routing operating on an MPLS data plane.  It defined Adj-
   SID Sub-TLV and LAN Adj-SID Sub-TLV advertised with Extended Link TLV
   defined in [RFC7684].  This document extends these two Sub-TLVs to
   carry the specific algorithm.



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3.2.1.  OSPF Adj-SID Sub-TLV

   The existing Adj-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   |   MT-ID       |  Weight       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   SID/Label/Index (variable)                  |
      +---------------------------------------------------------------+



                       Figure 3: OSPF Adj-SID Format

   where:

   Algorithm: The new Algorithm field contains the identifier of the
   algorithm the router uses to apply algorithm specific QoS policy
   configured on the adjacency.

   For a P2P link, an SR-capable router MAY allocate different Adj-SID
   for different algorithm, if this link will join different algorithm
   related plane.

3.2.2.  OSPF LAN Adj-SID Sub-TLV

   The existing LAN Adj-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   |     MT-ID     |    Weight     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Neighbor ID                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    SID/Label/Index (variable)                 |
      +---------------------------------------------------------------+



                     Figure 4: OSPF LAN Adj-SID Format




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   where:

   Algorithm: The new Algorithm field contains the identifier of the
   algorithm the router uses to apply algorithm specific QoS policy
   configured on the adjacency.

   For a broadcast link, an SR-capable router MAY allocate different
   Adj-SID for different algorithm, if this link will join different
   algorithm related plane.

3.3.  OSPFv3 Adjacency Segment Identifier per Algorithm

   [RFC8666] describes the OSPFv3 extensions that need to be introduced
   for Segment Routing operating on an MPLS data plane.  It defined Adj-
   SID Sub-TLV and LAN Adj-SID Sub-TLV advertised with Router-Link TLV
   as defined in [RFC8362].  This document extends these two Sub-TLVs to
   carry the specific algorithm.

3.3.1.  OSPFv3 Adj-SID Sub-TLV

   The existing Adj-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         |     Weight    |   Algorithm   |   Reserved    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   SID/Label/Index (variable)                  |
      +---------------------------------------------------------------+



                      Figure 5: OSPFv3 Adj-SID Format

   where:

   Algorithm: The new Algorithm field contains the identifier of the
   algorithm the router uses to apply algorithm specific QoS policy
   configured on the adjacency.

   For a P2P link, an SR-capable router MAY allocate different Adj-SID
   for different algorithm, if this link will join different algorithm
   related plane.






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3.3.2.  OSPFv3 LAN Adj-SID Sub-TLV

   The existing LAN Adj-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     |     Weight    |   Algorithm   |   Reserved    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Neighbor ID                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    SID/Label/Index (variable)                 |
      +---------------------------------------------------------------+



                    Figure 6: OSPFv3 LAN Adj-SID Format

   where:

   Algorithm: The new Algorithm field contains the identifier of the
   algorithm the router uses to apply algorithm specific QoS policy
   configured on the adjacency.

   For a broadcast link, an SR-capable router MAY allocate different
   Adj-SID for different algorithm, if this link will join different
   algorithm related plane.

4.  Operations

   The method introduced in this document enables the traffic of
   different flex-algo plane to be distinguished on the same link, so
   that these traffic can be applied with different QoS policy per
   algorithm.

   The endpoint of a link shared by multiple flex-algo plane can reserve
   different queue resources for different algorithms locally, and
   perform priority based queue scheduling and traffic shaping.  This
   algorithm related reserved information can be advertised to other
   nodes in the network through some mechanism, therefore it has an
   impact on the constraint based path calculation of the flex-algo
   plane.  How to allocate algorithm related resouce and advertise it in
   the network is out the scope of this document.

   The following figure shows an example of Adjacency-SID per algorithm.




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                        [S1]--------[D]--------[S2]
                         |           |          |
                         |           |          |
                         |           |          |
                        [A]---------[B]--------[C]


       Figure 7: Flex-algo LFA Path with Adjacency-SID per Algorithm

   Suppose that node S1, A, B, D and their inter-connected links belongs
   to FA-id 128 plane, and S2, B, C, D and their inter-connected links
   belongs to FA-id 129 plane.  The IGP metric of link B-D is 100, and
   all other links have IGP metric 1.  In FA-id 128 plane, from S1 to
   destination D, the primary path is S1-D, and the TI-LFA backup path
   is segment list {node(B), adjacency(B-D)}. Similarly, In FA-id 129
   plane, from S2 to destination D, the primary path is S2-D, and the
   TI-LFA backup path is segment list {node(B), adjacency(B-D)}. The
   above TI-LFA path of FA-id 128 plane can be translated to {node-
   SID(B)@FA-id128, adjacency-SID(B-D)@FA-id128}, and TI-LFA path of FA-
   id 129 plane will be translate to {node-SID(B)@FA-id129, adjacency-
   SID(B-D)@FA-id129}. So that node B can distinguish the flow of FA-id
   128 and FA-id 129 based on different adjacency-SID(B-D), and take
   different treatment (e.g., QoS policy) of them when they are send to
   the same outgoing link B-D.

5.  IANA Considerations

   TBD

6.  Security Considerations

   There are no new security issues introduced by the extensions in this
   document.

7.  Acknowledgements

   TBD

8.  Normative References

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-11 (work in progress), September 2020.







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   [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>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <https://www.rfc-editor.org/info/rfc4915>.

   [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,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

   [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>.

   [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>.



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   [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>.

   [RFC8668]  Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
              M., and E. Aries, "Advertising Layer 2 Bundle Member Link
              Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
              December 2019, <https://www.rfc-editor.org/info/rfc8668>.

Authors' Addresses

   Peng Shaofu
   ZTE Corporation
   No.68 Zijinghua Road, Yuhuatai District
   Nanjing
   China

   Email: peng.shaofu@zte.com.cn


   Chen Ran
   ZTE Corporation
   No.50 Software Avenue, Yuhuatai District
   Nanjing
   China

   Email: chen.ran@zte.com.cn






















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