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

IDR Working Group                                                A. Wang
Internet-Draft                                             China Telecom
Intended status: Standards Track                                 H. Chen
Expires: October 10, 2019                            Huawei Technologies
                                                                   S. Ma
                                                   Mellanox Technologies
                                                           April 8, 2019


            BGP-LS Extension for Inter-AS Topology Retrieval
             draft-ietf-idr-bgpls-inter-as-topology-ext-02

Abstract

   This document describes the process to build BGP-LS key parameters in
   multi-domain scenario, defines one new BGP-LS NLRI type(Stub 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 interconnect 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
   working documents as Internet-Drafts.  The list of current Internet-
   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 October 10, 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
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   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
   4.  Stub Link NLRI  . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Inter-AS Native IP Scenario . . . . . . . . . . . . . . .   4
     4.2.  Inter-AS TE Scenario  . . . . . . . . . . . . . . . . . .   4
   5.  Inter-AS TE NLRI related TLVs . . . . . . . . . . . . . . . .   5
     5.1.  Remote AS Number TLV  . . . . . . . . . . . . . . . . . .   5
     5.2.  IPv4 Remote ASBR ID . . . . . . . . . . . . . . . . . . .   6
     5.3.  IPv6 Remote ASBR ID . . . . . . . . . . . . . . . . . . .   7
   6.  Topology Reconstruction.  . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   8
   10. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

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 mechanic 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 interconnected topology information between different AS
   domains, defines the new Stub 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
   discusses.  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

4.  Stub 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 link, the two ends of the link



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   locates in different IGP domains, then it is not appropriate to
   transfer their information within the current defined NLRI types.

   This draft defines one new NLRI type, called Stub 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 2: The Inter-AS TE Link NLRI Format

   The semantics of "Stub Link Descriptors" is same as that defined in
   [RFC7752] for "Link Descriptor".

   This newly defined NLRI can be used to describe the link that has
   only one end located within the IGP domain, as described in the
   following sections.

4.1.  Inter-AS Native IP Scenario

   When IGP A or IGP B runs native IS-IS/OSPF protocol, the operator can
   use passive feature for the inter-domain links to let the routers
   within the IGP domain know these links.  Such stub links information
   can then be carried within the Stub Link NLRI to be reported via the
   BGP-LS protocol to the SDN controller.

   The "Local Node Descriptors" should describe the the characteristics
   of ASBRs that are connected these stub links.

   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.

4.2.  Inter-AS TE Scenario

   When IGP A or IGP B run IS-IS TE/OSPF-TE protocol, [RFC5316] and
   [RFC5392] define the IS-IS and OSPF extensions respectively to deal
   with the situation for inter-AS traffic engineering.  Three new sub-



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   TLVs(Remote AS Number、IPv4 Remote ASBR ID、IPv6 Remote
   ASBR ID) which are associated with the inter-AS TE link are defined.

   These TLVs are flooded within the IGP domain automatically.  They can
   also be carried within the newly defined Stub Link NLRI within the
   BGP-LS protocol, as the descriptors for the inter-AS stub link.

   The "Local Node Descriptors" should describe the the characteristics
   of ASBRs that are connected these inter-AS TE links.

   If the PCE/SDN controller 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 according to the procedure
   described in section 6

5.  Inter-AS TE NLRI related TLVs

   This draft proposes to add three new TLVs that is included within the
   Stub Link NLRI to transfer the information via BGP-LS, which are
   required to build the inter-AS TE related topology by the PCE/SDN
   controller.

   The following Link Descriptor TLVs are added into the 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 3: Link Descriptor TLVs

   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.



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   The remote AS number TLV is TLV type TBD (see Section 8) 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 4: 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.

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 8) 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 5:  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.






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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 8) and is 16
   octets in length.  The format of the IPv6 remote ASBR ID 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                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Remote ASBR ID (continued)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 6:  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 these stub links.  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 stub links, the
   SDN controller can then retrieve the connection topology between
   different domains automatically.





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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 which spans MAN-
   backbone-IDC, they need to know the inter-as topology via the process
   described in this draft.  Using the passive interface features or
   configuring the TE parameters on the interconnect links will not
   spread the topology fluctuation across each other domain.

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-12
              (work in progress), March 2019.

   [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-18 (work in progress), March 2019.

   [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>.



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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>.

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

   [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







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

   Email: wangaj.bri@chinatelecom.cn


   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   Email: Huaimo.chen@huawei.com


   Shaowen Ma
   Mellanox Technologies

   Email: mashaowen@gmail.com






























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