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Versions: (draft-wang-idr-bgpls-inter-as-topology-ext) 00 01 02 03

IDR Working Group                                                A. Wang
Internet-Draft                                             China Telecom
Intended status: Standards Track                                 H. Chen
Expires: September 8, 2019                           Huawei Technologies
                                                                   S. Ma
                                                        Juniper Networks
                                                           March 7, 2019


            BGP-LS Extension for Inter-AS Topology Retrieval
             draft-ietf-idr-bgpls-inter-as-topology-ext-01

Abstract

   This document describes the process to build BGP-LS key parameters in
   multi-domain scenario, defines one new BGP-LS NLRI type(Inter-AS TE
   Link NLRI) and some new inter-AS TE related TLVs for BGP-LS to let
   SDN controller retrieve the network topology automatically under
   various environments.

   Such process and extension can enable the network operator to collect
   the connection information between different domains and then
   calculate the overall network topology automatically based on the
   information provided by BGP-LS protocol.

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 September 8, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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
   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.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  Inter-AS Domain Scenarios.  . . . . . . . . . . . . . . . . .   3
     3.1.  IS-IS/OSPF Inter-AS Native IP Scenario  . . . . . . . . .   4
     3.2.  IS-IS/OSPF Inter-AS TE Scenario . . . . . . . . . . . . .   5
   4.  Inter-AS TE Link NLRI . . . . . . . . . . . . . . . . . . . .   5
   5.  Inter-AS TE NLRI related TLVs . . . . . . . . . . . . . . . .   5
     5.1.  Remote AS Number TLV  . . . . . . . . . . . . . . . . . .   6
     5.2.  IPv4 Remote ASBR ID . . . . . . . . . . . . . . . . . . .   7
     5.3.  IPv6 Remote ASBR ID . . . . . . . . . . . . . . . . . . .   7
   6.  Topology Reconstruction.  . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   9
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   BGP-LS [RFC7752] describes the methodology that using BGP protocol to
   transfer the Link-State information.  Such method can enable SDN
   controller to collect the underlay network topology automatically,
   but normally it can only get the information within one IGP domain.
   If the operator has more than one IGP domain, and these domains
   interconnect with each other, there is no general TLV within current
   BGP- LS to transfer the interconnect topology information.

   Draft [I-D.ietf-idr-bgpls-segment-routing-epe] defines some
   extensions for exporting BGP peering node topology information
   (including its peers, interfaces and peering ASs) in a way that is
   exploitable in order to compute efficient BGP Peering Engineering
   policies and strategies.  Such information can also be used to
   calculate the interconnection topology among different IGP domains,
   but it requires the border routers to run BGP-LS protocol and report
   the information to the PCE/SDN controller, which restricts the
   solution deployment flexibility.



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   This draft analysis the situations that the PCE/SDN controller needs
   to get the inter-connected topology information between different AS
   domains, defines the new Inter-AS TE Link NLRI and some new TLVs
   within the BGP-LS protocol to transfer the key information related to
   them.  After that, the SDN controller can then deduce the multi-
   domain topology automatically based on the information from BGP-LS
   protocol.

2.  Conventions used in this document

   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] .

3.  Inter-AS Domain Scenarios.

   Fig.1 illustrates the multi-domain scenarios that this draft
   discussed.  Normally, SDN Controller can get the topology of IGP A
   and IGP B individually via the BGP-LS protocol, but it can't get the
   topology connection information between these two IGP domains because
   there is generally no IGP protocol run on the connected links.

                             +-----------------+
                        +----+IP SDN Controller+----+
                        |    +-----------------+    |
                        |                           |
                        |BGP-LS                     |BGP-LS
                        |                           |
        +---------------+-----+               +-----+--------------+
        | +--+        +-++   ++-+           +-++   +|-+        +--+|
        | |S1+--------+S2+---+B1+-----------+B2+---+T1+--------+T2||
        | +-++   N1   +-++   ++-+           +-++   ++++   N2   +-++|
        |   |           |     |               |     ||           | |
        |   |           |     |               |     ||           | |
        | +-++        +-++   ++-+           +-++   ++++        +-++|
        | |S4+--------+S3+---+B3+-----------+B4+---+T3+--------+T4||
        | +--+        +--+   ++-+           +-++   ++-+        +--+|
        |                     |               |                    |
        |                     |               |                    |
        |       IGP A         |               |      IGP B         |
        +---------------------+               +--------------------+

                    Figure 1: Inter-AS Domain Scenarios








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3.1.  IS-IS/OSPF Inter-AS Native IP Scenario

   When the IGP A or IGP B runs native IS-IS/OSPF protocol, the operator
   can redistributes the IPv4/IPv6 prefixes of interconnect links into
   IS-IS/OSPF protocol to ensure the inter-domain connectivity.

   If the IGP runs IS-IS protocol, the redistributed link information
   will be carried in IP External Reachability Information TLV within
   the Level 2 PDU type that defined in [RFC1195], every router within
   the IGP domain can deduce the redistributed router from the IS-IS
   LSDB.

   If the IGP runs OSPF protocol[RFC2328]defines the type 5 external LSA
   to transfer the external IPv4 routes;
   [I-D.ietf-ospf-ospfv3-lsa-extend] defines the "External-Prefix TLV"
   to transfer the external IPv6 routes; these LSAs have also the
   advertising router information that initiates the redistribute
   activity.  Every router within IGP domain can also deduce the
   redistributed router from the OSPF LSDB.

   For prefix information that associated with each router, BGP-LS
   [RFC7752] defines the Prefix NLRI which is illustrated below:

        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
       +-+-+-+-+-+-+-+-+
       |  Protocol-ID  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Identifier                          |
       |                            (64 bits)                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //              Local Node Descriptors (variable)              //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                Prefix Descriptors (variable)                //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 2: The IPv4/IPv6 Topology Prefix NLRI Format

   For these redistributed inter-domain links, their prefix information
   should be included in the "Prefix Descriptor", and the associated
   redistributed router information should be included in the "Local
   Node Descriptors".

   When such information is reported via the BGP-LS protocol, the PCE/
   SDN controller can construct the underlay inter-domain topology
   according to procedure described in section 6.





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3.2.  IS-IS/OSPF Inter-AS TE Scenario

   [RFC5316] and [RFC5392] define the IS-IS and OSPF extensions
   respectively to deal with the requirements for inter-AS traffic
   engineering.  They define some new sub-TLVs(Remote AS
   Number、IPv4 Remote ASBR ID、IPv6 Remote ASBR ID) which
   are associated with the inter-AS TE link TLVs to report the TE
   topology between different domains.

   These TLVs are flooded within the IGP domain automatically.  If the
   PCE/SDN controller can know these information via one of the interior
   router that runs BGP-LS protocol, the PCE/SDN controller can rebuild
   the inter-AS TE topology correctly.

4.  Inter-AS TE Link NLRI

   [RFC7752] defines four NLRI types(Node NLRI, Link NLRI, IPv4 Topology
   Prefix NLRI, IPv6 Topology Prefix NLRI) to transfer the topology and
   prefix information.  For inter-as TE link, the two ends of the link
   locates in different IGP domains, then it is not appropriate to
   transfer their information within the current defined NLRI types.

   This draft defines then one new NLRI type, called Inter-AS TE Link
   NLRI, which is coded as 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
       +-+-+-+-+-+-+-+-+
       |  Protocol-ID  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Identifier                          |
       |                            (64 bits)                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //              Local Node Descriptors (variable)              //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //            Inter-AS TE Link Descriptors (variable)          //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 3: The Inter-AS TE Link NLRI Format

   The semantics of "Inter-AS TE Link Descriptors" is same as that
   defined in [RFC7752] for "Link Descriptor".

5.  Inter-AS TE NLRI related TLVs

   This draft proposes to add three new TLVs that is included within the
   inter-AS TE Link NLRI to transfer the information via BGP-LS, which




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   are required to build the inter-AS related topology by the PCE/SDN
   controller.

   The following Link Descriptor TLVs are added into the Inter-AS TE
   Link NLRI in BGP-LS protocol :

   +-----------+---------------------+--------------+----------------+
   |  TLV Code | Description         |IS-IS/OSPF TLV| Reference      |
   |   Point   |                     |   /Sub-TLV   | (RFC/Section)  |
   +-----------+---------------------+--------------+----------------+
   |    TBD    |Remote AS Number     |   24/21      | [RFC5316]/3.3.1|
   |           |                     |              | [RFC5392]/3.3.1|
   |    TBD    |IPv4 Remote ASBR ID  |   25/22      | [RFC5316]/3.3.2|
   |           |                     |              | [RFC5392]/3.3.2|
   |    TBD    |IPv6 Remote ASBR ID  |   26/24      | [RFC5316]/3.3.3|
   |           |                     |              | [RFC5392]/3.3.3|
   +-----------+---------------------+--------------+----------------+
     Figure 4: Link Descriptor TLVs for Inter-AS TE Link NLRI Format

   Detail encoding of these TLVs are synchronized with the corresponding
   parts in [RFC5316] and [RFC5392], which keeps the BGP-LS protocol is
   agnostic to the underly protocol.

5.1.  Remote AS Number TLV

   A new TLV, the remote AS number TLV, is defined for inclusion in the
   link descriptor when advertising inter-AS TE links.  The remote AS
   number TLV specifies the AS number of the neighboring AS to which the
   advertised link connects.

   The remote AS number TLV is TLV type TBD (see Section 7) and is 4
   octets in length.  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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote AS Number                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 5: Remote AS Number TLV Format

   The Remote AS number field has 4 octets.  When only 2 octets are used
   for the AS number, as in current deployments, the left (high-order) 2
   octets MUST be set to 0.  The remote AS number TLV MUST be included
   when a router advertises an inter-AS TE link.





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5.2.  IPv4 Remote ASBR ID

   A new TLV, which is referred to as the IPv4 remote ASBR ID TLV, is
   defined for inclusion in the link descriptor when advertising inter-
   AS TE links.  The IPv4 remote ASBR ID TLV specifies the IPv4
   identifier of the remote ASBR to which the advertised inter-AS link
   connects.  This could be any stable and routable IPv4 address of the
   remote ASBR.  Use of the TE Router ID as specified in the Traffic
   Engineering router ID TLV [RFC5305] is RECOMMENDED.

   The IPv4 remote ASBR ID TLV is TLV type TBD (see Section 7) and is 4
   octets in length.  The format of the IPv4 remote ASBR ID sub-TLV 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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 6:  IPv4 Remote ASBR ID TLV Format

   The IPv4 remote ASBR ID TLV MUST be included if the neighboring ASBR
   has an IPv4 address.  If the neighboring ASBR does not have an IPv4
   address (not even an IPv4 TE Router ID), the IPv6 remote ASBR ID TLV
   MUST be included instead.  An IPv4 remote ASBR ID TLV and IPv6 remote
   ASBR ID TLV MAY both be present in an inter-AS TE link NLRI.

5.3.  IPv6 Remote ASBR ID

   A new TLV, which is referred to as the IPv6 remote ASBR ID TLV, is
   defined for inclusion in the inter-AS reachability TLV when
   advertising inter-AS links.  The IPv6 remote ASBR ID TLV specifies
   the IPv6 identifier of the remote ASBR to which the advertised inter-
   AS link connects.  This could be any stable and routable IPv6 address
   of the remote ASBR.  Use of the TE Router ID as specified in the IPv6
   Traffic Engineering router ID TLV [RFC6119] is RECOMMENDED.

   The IPv6 remote ASBR ID TLV is TLV type TBD (see Section 7) and is 16
   octets in length.  The format of the IPv6 remote ASBR ID TLV 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            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 7:  IPv6 Remote ASBR ID TLV Format

   The IPv6 remote ASBR ID TLV MUST be included if the neighboring ASBR
   has an IPv6 address.  If the neighboring ASBR does not have an IPv6
   address, the IPv4 remote ASBR ID TLV MUST be included instead.  An
   IPv4 remote ASBR ID TLV and IPv6 remote ASBR ID TLV MAY both be
   present in an inter-AS TE link NLRI.

6.  Topology Reconstruction.

   When SDN Controller gets such information from BGP-LS protocol, it
   should compares the proximity of the redistributed prefixes.  If they
   are under the same network scope, then it should find the
   corresponding associated router information, build the link between
   these two border routers.

   After iterating the above procedures for all of the redistributed
   prefixes, the SDN controller can then retrieve the connection
   topology between different domains automatically.

7.  Security Considerations

   It is common for one operator to occupy several IGP domains that are
   composited by its backbone network and several MAN(Metrio-Area-
   Network)s/IDCs.  When they do traffic engineering from end to end
   that spans MAN-backbone-IDC, they need to know the inter-as topology
   via the process described in this draft.  Then it is naturally to
   redistribute the interconnection prefixes in Native IP scenario.

   If these IGP domains belong to different operators, it is uncommon do
   inter-as traffic engineering under one PCE/SDN controller, then it is
   unnecessary to get the inter-as topology.  But redistributing the
   interconnection prefixes will do no harm to their networks, because
   the redistributed interconnection link prefixes belongs to both of
   them, they are also the interfaces addresses on the border routers. .



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8.  IANA Considerations

   TBD.

9.  Acknowledgement

   The author would like to thank Acee Lindem, Ketan Talaulikar, Jie
   Dong, Jeff Tantsura and Dhruv Dhody for their valuable comments and
   suggestions.

10.  Normative References

   [I-D.ietf-idr-bgp-ls-segment-routing-ext]
              Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
              and M. Chen, "BGP Link-State extensions for Segment
              Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-11
              (work in progress), October 2018.

   [I-D.ietf-idr-bgpls-segment-routing-epe]
              Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
              S., and J. Dong, "BGP-LS extensions for Segment Routing
              BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
              segment-routing-epe-17 (work in progress), October 2018.

   [I-D.ietf-ospf-ospfv3-lsa-extend]
              Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
              Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
              lsa-extend-23 (work in progress), January 2018.

   [I-D.ietf-teas-native-ip-scenarios]
              Wang, A., Huang, X., Qou, C., Li, Z., and P. Mi,
              "Scenario, Simulation and Suggestion of PCE in Native IP
              Network", draft-ietf-teas-native-ip-scenarios-02 (work in
              progress), October 2018.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <https://www.rfc-editor.org/info/rfc1195>.

   [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>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.




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   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <https://www.rfc-editor.org/info/rfc5305>.

   [RFC5316]  Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
              December 2008, <https://www.rfc-editor.org/info/rfc5316>.

   [RFC5392]  Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
              Support of Inter-Autonomous System (AS) MPLS and GMPLS
              Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392,
              January 2009, <https://www.rfc-editor.org/info/rfc5392>.

   [RFC6119]  Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
              Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
              February 2011, <https://www.rfc-editor.org/info/rfc6119>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
              and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
              March 2016, <https://www.rfc-editor.org/info/rfc7794>.

   [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>.

Authors' Addresses

   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing, Beijing  102209
   China

   Email: wangaj.bri@chinatelecom.cn








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   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   Email: Huaimo.chen@huawei.com


   Shaowen Ma
   Juniper Networks

   Email: mashao@juniper.net







































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