BESS WorkGroup                                           S. Agrawal, Ed.
Internet-Draft                                                    D. Rao
Intended status: Standards Track                                  Z. Ali
Expires: 27 April 2023                                       C. Filsfils
                                                           Cisco Systems
                                                                D. Voyer
                                                             Bell Canada
                                                                G. Dawra
                                                                LinkedIn
                                                                   Z. Li
                                                     Huawei Technologies
                                                         24 October 2022


             BGP extensions for SRv6 and MPLS interworking
            draft-agrawal-bess-bgp-srv6-mpls-interworking-00

Abstract

   This document define the BGP protocol extensions required to provide
   interworking between SRv6 and SR-MPLS/MPLS for SRv6 deployment.

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
   and may be updated, replaced, or obsoleted by other documents at any
   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 27 April 2023.

Copyright Notice

   Copyright (c) 2022 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 carefully, as they describe your rights



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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  SRv6 SID advertisement in BGP update for PE address . . . . .   3
     2.1.  SRv6 tunnel for label route TLV . . . . . . . . . . . . .   3
     2.2.  SRv6 SID bound to prefix in NLRI  . . . . . . . . . . . .   4
       2.2.1.  Address in NLRI is only bound to SRv6 SID . . . . . .   4
       2.2.2.  MPLS label and SRv6 SID bound to prefix in NLRI . . .   5
     2.3.  Propogation of SRv6 SID in BGP update for PE address  . .   6
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  BGP Prefix-SID TLV Types registry . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The deployment of SRv6 into existing networks require SRv6 to
   interwork with SR-MPLS/MPLS.  Draft
   [I-D.agrawal-spring-srv6-mpls-interworking] describes SRv6 and MPLS
   interworking architecture in multi domain network where each domain
   run SRv6 or MPLS data plane independently.  Specifically section
   7.1.2 of draft details BGP inter-domain routing procedures to
   advertise PE locators or PE loopbacks address across such network
   with next hop self at domain border routers.  When performing next
   hop self on domain border router and further propagation, draft
   proposes to allocate and signal additional upstream data plane
   specific information.  This document extract the BGP protocol
   extensions proposed in [I-D.agrawal-spring-srv6-mpls-interworking] to
   signal SRv6 SID with BGP SAFI 4 or SAFI 1 advertisements.  This is
   done to independently state BGP protocol extensions and future
   applicability of them for other use cases.










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1.1.  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.

2.  SRv6 SID advertisement in BGP update for PE address

   [RFC9252] extended BGP Prefix SID Attribute (PFA) to signal SRv6 SID
   in "SRv6 L3 Service" and "SRv6 L2 Service" TLVs for layer 3 and layer
   2 services.  This document introduces new "SRv6 tunnel for label
   route" TLV for safi 4 [RFC8277] and extends usage of "SRv6 L3
   Service" TLV for SAFI 4.

2.1.  SRv6 tunnel for label route TLV

   [RFC8669] introduced Prefix-SID attribute with TLV type 1 for label
   index and TLV type 3 for Originator SRGB for AFI=1/2 and SAFI 4 (BGP
   LU).  This document introduces a new TLV called "SRv6 tunnel for
   label route" of the BGP Prefix-SID Attribute to signal SRv6 SIDs
   along with MPLS label bound to prefix in NLRI.  Behavior that may be
   encoded but not limited to is End.DTM.  "SRv6 tunnel for label route"
   TLV signals "AND" semantics i.e.  push label signaled in NLRI and
   perform H.Encaps.M with DA as SRv6 SID signaled in TLV.  This
   document limits the usage of this new TLV to AFI=1/2 SAFI 4.  The
   usage of this TLV for other AFI/SAFI is out of scope of this
   document.

   "SRv6 tunnel for label route" TLV is encoded exactly like SRv6
   Service TLVs in Prefix-SID Attribute [RFC9252] with following
   modification:

   *  TLV Type (1 octet): This field is assigned values from the IANA
      registry "BGP Prefix-SID TLV Types".  It is set to 7 for "SRv6
      tunnel for label route" TLV.

   *  No transposition scheme is allowed i.e. transposition length MUST
      be 0 in SRv6 SID Structure Sub-Sub-TLV.

   Please refer to section 7.1.2.2.1 of
   [I-D.agrawal-spring-srv6-mpls-interworking] for usage of "SRv6 tunnel
   for label route" TLV and overall procedures along with control and
   forwarding state






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2.2.  SRv6 SID bound to prefix in NLRI

   Bound the SRv6 SID of DPM behavior to PE loopback address carried in
   NLRI of BGP update of SAFI 1 or SAFI 4.  Receiving node perform
   H.Encaps, where destination of IPv6 header is set to SRv6 SID for
   traffic destined to address in NLRI.

   Please refer to section 7.1.2.2.2 of
   [I-D.agrawal-spring-srv6-mpls-interworking] for overall procedures
   when SRv6 SID is bound to PE address.

   This document proposes below 2 options to advertise SRv6 SID bound to
   prefix in NLRI

2.2.1.  Address in NLRI is only bound to SRv6 SID

   Address in NLRI is only bound to SRv6 SID by advertising node.  In
   this case, SAFI 4 cannot be used to advertise PE loopback across SRv6
   domain as label is required in NLRI [RFC8277].  Therefore SRv6 SID
   with End.DPM behavior bound to prefix in NLRI is advertised in SAFI 1
   as per section 5.3 and 5.4 of [RFC9252].  To distinguish from global
   internet routes on receiver, local policy matching PE loopback
   addresses or BGP community/extended community attached to such
   advertisement may be used.  Such policy on receiver helps to allocate
   MPLS label and advertise route further upstream in SAFI 4 in MPLS
   domain for PE addresses with next hop self.  Figure 1 shows BGP
   update example through SRv6 domain.
























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          +-----+                +-----+  RD:V/v via 10   +-----+
   .......|S-RR1|<...............|S-RR2|<.................|S-RR3| <..
   :      +-----+                +-----+                  +-----+   :
   :                                                                :
   :                                                                :
+--:-------------------+----------------------+---------------------:-+
|  :                   |                      |                     : |
|  :                   |                      |                     : |
|  :       SAFI 4      |       SAFI 1         |      SAFI 4         : |
|  : <-E10,Label via 4 |   <-E10 via 7        |  <-E10,0x3 via E10  : |
|  :                   |   SRv6 SID=B7:E10::  |                     : |
|----+               +---+                  +---+                +----|
| E1 |               | 4 |                  | 7 |                |E10 |
|----+               +---+                  +---+                +----|
|                      |                      |                       |
|                      |                      |                       |
|                      |                      |                       |
|                      |                      |                       |
|        MPLS          |        SRv6          |       MPLS            |
+----------------------+----------------------+-----------------------+
iPE                   iBR                    eBR                     ePE

<----------LI---------><----------C----------><-----------LE---------->

              Figure 1: SRv6 SID bound to NLRI of SAFI 1

2.2.2.  MPLS label and SRv6 SID bound to prefix in NLRI

   Advertise MPLS label and SRv6 SID bound to prefix in NLRI.  RFC 8669
   introduced Prefix-SID attribute with TLV type 1 for label index and
   TLV type 3 for Originator SRGB for AFI=1/2 and SAFI 4 (BGP LU).  This
   document extends the BGP Prefix-SID attribute [RFC8669] to carry
   "SRv6 L3 Service TLV" defined in [RFC9252] with AFI=1/2 and SAFI 4.
   TLV is encoded exactly like SRv6 Service TLVs in Prefix-SID Attribute
   without transposition.  Such an update can be processed by both
   legacy MPLS ABR and SRv6 capable ABR and use relevant encapsulation.
   For example, in Figure 2 node 4 being SRv6 capable chooses SRv6
   encapsulation and node 44 being legacy continue MPLS encapsulation.













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          +-----+                +-----+  RD:V/v via 10   +-----+
   .......|S-RR1|<...............|S-RR2|<.................|S-RR3| <..
   :      +-----+                +-----+                  +-----+   :
   :                                                                :
   :                                                                :
+--:-------------------+----------------------+---------------------:-+
|  :                   |                      |                     : |
|  :                 +---+                    |                     : |
|  :                 | 4 |                    |                     : |
|  :     SAFI 4      +---+    SAFI 4          |      SAFI 4         : |
|  : <-E10,Label via 4 |  <-E10,Label via 7   |   <-E10,0x3 via E10 : |
|----+                 |  SRv6 SID=B7:E10:: +---+                +----|
| E1 |                 |                    | 7 |                |E10 |
|----+               +---+                  +---+                +----|
|                    |44 |                    |                       |
|                    +---+                    |                       |
|                      |                      |                       |
|                      |                      |                       |
|        MPLS          |        SRv6/MPLS     |       MPLS            |
+----------------------+----------------------+-----------------------+
iPE                   iBR                    eBR                     ePE

<----------LI---------><----------C----------><-----------LE---------->

              Figure 2: SRv6 SID bound to NLRI of SAFI 4

2.3.  Propogation of SRv6 SID in BGP update for PE address

   A BGP speaker receiving updates with PE address in NLRI and Prefix-
   SID Attribute with "SRv6 tunnel for label route" TLV or "SRv6 L3
   Service" TLV observe the following rules when advertising the route
   to other peers:

   *  If the nexthop is unchanged, the TLVs, including any unrecognized
      Types of Sub-TLV and Sub-Sub-TLV, SHOULD be propagated further.
      In addition, all Reserved fields in the TLV or Sub-TLV or Sub-Sub-
      TLV MUST be propagated unchanged.

   *  If the nexthop is modified, the TLV and associated sub-TLVs/Sub-
      Sub-TLVs SHOULD be updated based on local policy.  For example, if
      upstream is MPLS domain, then TLVs carrying SRv6 SID should be
      removed and local MPLS label bound to address in NLRI is sent in
      SAFI 4.

3.  IANA Considerations






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3.1.  BGP Prefix-SID TLV Types registry

   This document introduce a new TLV Type of the BGP Prefix-SID
   attribute.  IANA is requested to assign Type value in the registry
   "BGP Prefix-SID TLV Types" as follows

       Value     Type                             Reference
       ----------------------------------------------------------
       TBD       "SRv6 tunnel for label route" TLV     <this document>

4.  Security Considerations

5.  Acknowledgements

   The authors would like to acknowledge Stephane Litkowski and Ketan
   Talaulikar for review and comments.

6.  References

6.1.  Normative References

   [I-D.agrawal-spring-srv6-mpls-interworking]
              Agrawal, S., ALI, Z., Filsfils, C., Voyer, D., and H.
              Technologies, "SRv6 and MPLS interworking", Work in
              Progress, Internet-Draft, draft-agrawal-spring-srv6-mpls-
              interworking-09, 8 September 2022,
              <https://www.ietf.org/archive/id/draft-agrawal-spring-
              srv6-mpls-interworking-09.txt>.

   [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-22, 22 March 2022,
              <https://www.ietf.org/archive/id/draft-ietf-spring-
              segment-routing-policy-22.txt>.

   [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>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.





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   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
              "Encapsulating MPLS in IP or Generic Routing Encapsulation
              (GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
              <https://www.rfc-editor.org/info/rfc4023>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
              Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
              Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
              2015, <https://www.rfc-editor.org/info/rfc7432>.

   [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>.

   [RFC8277]  Rosen, E., "Using BGP to Bind MPLS Labels to Address
              Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
              <https://www.rfc-editor.org/info/rfc8277>.

   [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>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

   [RFC8669]  Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
              A., and H. Gredler, "Segment Routing Prefix Segment
              Identifier Extensions for BGP", RFC 8669,
              DOI 10.17487/RFC8669, December 2019,
              <https://www.rfc-editor.org/info/rfc8669>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/info/rfc8986>.







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   [RFC9252]  Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
              B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
              Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
              DOI 10.17487/RFC9252, July 2022,
              <https://www.rfc-editor.org/info/rfc9252>.

6.2.  Informative References

   [I-D.ietf-mpls-seamless-mpls]
              Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
              M., and D. Steinberg, "Seamless MPLS Architecture", Work
              in Progress, Internet-Draft, draft-ietf-mpls-seamless-
              mpls-07, 28 June 2014, <https://www.ietf.org/archive/id/
              draft-ietf-mpls-seamless-mpls-07.txt>.

Authors' Addresses

   Swadesh Agrawal (editor)
   Cisco Systems
   Email: swaagraw@cisco.com


   Dhananjaya Rao
   Cisco Systems
   Email: dhrao@cisco.com


   Zafar ALI
   Cisco Systems
   Email: zali@cisco.com


   Clarence Filsfils
   Cisco Systems
   Email: cfilsfil@cisco.com


   Daniel Voyer
   Bell Canada
   Canada
   Email: daniel.voyer@bell.ca


   Gaurav dawra
   LinkedIn
   United States of America
   Email: gdawra.ietf@gmail.com




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   Zhenbin Li
   Huawei Technologies
   China
   Email: lizhenbin@huawei.com















































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