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BESS WG                                                         Z. Zhang
Internet-Draft                                                   S. Peng
Intended status: Standards Track                               G. Mirsky
Expires: February 14, 2021                                       Y. Wang
                                                         ZTE Corporation
                                                         August 13, 2020


               SRv6 and MPLS interworking for VPN service
                  draft-pzm-spring-interdomain-vpn-02

Abstract

   This document describes a method to achieve an inter-domain
   connection for a VPN (Virtual Private Network) service.

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
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   This Internet-Draft will expire on February 14, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   2
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Theory of operation . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  SRv6 to SR-MPLS domain signaling  . . . . . . . . . . . .   3
     3.2.  SR-MPLS to SRv6 domain signaling  . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   [I-D.agrawal-spring-srv6-mpls-interworking] describes SRv6 and MPLS/
   SR-MPLS interworking and co-existence procedures.  The document
   leverages the function defined in
   [I-D.ietf-spring-srv6-network-programming] to give guidance to the
   forwarding in routers.

   [RFC4364] describes a method by which a Service Provider may use an
   IP backbone to provide IP Virtual Private Networks (VPNs) for its
   customers.  When SRv6 and SR-MPLS are co-existed in the backbone,
   controller or a control plane, for example, using BGP, should be used
   to instantiate the VPN service as described in
   [I-D.agrawal-spring-srv6-mpls-interworking].

   In case of option B inter-domain interconnection [RFC4364], only ASBR
   needs to do the stitching work between two ASes.  Thus PEs in SRv6
   and SR-MPLS domains do not have to support both SRv6 and SR-MPLS
   functions.  This document discusses the use of BGP for achieving VPN
   service through option B defined in [RFC4364] across a backbone that
   includes SRv6 and SR-MPLS domains.

2.  Conventions used in this document

2.1.  Terminology

   ASBR - Autonomous System Boundary Router

   PE - Provider's Equipment

   AS - Autonomous System




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   SR - Segment Routing

   SRv6 - Segment Routing over IPv6 data plane

   SR-MPLS - Segment Routing over MPLS data plane

   SID - Segment Identifier

   IMET - Inclusive Multicast Ethernet Tag

2.2.  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.  Theory of operation

3.1.  SRv6 to SR-MPLS domain signaling

   [I-D.ietf-bess-srv6-services] defines the new TLVs for the BGP
   Prefix-SID Attribute that can be used to signaling of SRv6 SID for L3
   and L2 services.  In this document, we use L3 case as the example,
   for the SRv6 SID without any arguments, the procedures for L2 are the
   same as in L3 scenario.

   We use Inclusive Multicast Ethernet Tag (IMET) routes as the example
   for the SRv6 SIDs with arguments.

                   +-------------+         +-------------+
                   |    AS1      |         |     AS2     |
                   |             |         |             |
         CE1+----+PE1          ASBR1+---+ASBR2          PE2+----+CE2
                   |             |         |             |
                   |    SRV6     |         |   SR-MPLS   |
                   +-------------+         +-------------+
                          Figure 1

   For example, CE1 and CE2 are connected through a backbone that
   includes AS1 and AS2.  AS1 supports SRv6 only, and AS2 supports SR-
   MPLS only.  ASBR1 supports both SRv6 and SR-MPLS capabilities, but
   ASBR2 supports SR-MPLS capability only.

   For a prefix advertised by CE1 to PE1, PE1 assigns SID with End.DT4
   (or End.DT6/DT46) defined in
   [I-D.ietf-spring-srv6-network-programming] section 4 (e.g., End.DT4



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   is used while the prefix is IPv4 prefix, End.DT6 is used while the
   prefix is IPv6 prefix), and advertises it to ASBR1.  Because ASBR2
   supports SR-MPLS function only, the SRv6 SID advertised by ASBR1
   cannot be executed by ASBR2.

   ASBR1 uses specific execution function that is different from the
   function used in a single SRv6 domain or a single SR-MPLS domain.  In
   this situation, ASBR1 assigns an MPLS label for the prefix or IMET
   routes received from PE1 and advertises it to ASBR2.  The MPLS label
   has local significance that indicates this packet is associated with
   an SRv6 SID list which leads the packet from ASBR1 to PE1.  The
   advertisement is the same as the format in [RFC4364] and [RFC4659]
   for L3VPN, and [I-D.heitz-bess-evpn-option-b] for EVPN.

   When a data flow packet which has the destination to CE1 is received
   by ASBR1, ASBR1 recognizes the MPLS label, removes the recognized
   label and adds an SRH to the packet, then forwards it to PE1.  Note
   that the SRH is needed when the packet continues to enter an outer
   SRv6 policy from headend ASBR1 to endpoint PE1, otherwise only an
   IPv6 header without SRH is encapsulated.

   When the recognized label is assigned to an IMET route, and the
   Argument Length of the SRv6 SID Structure Sub-Sub-TLV of the IMET
   route is not zero, the value of the label immediately after the
   recognized label is assigned to the argument part of the innermost
   SRv6 SID of the SRH before ASRB1 forwards it to PE1.

3.2.  SR-MPLS to SRv6 domain signaling

   In the same example, PE2 advertises a prefix received from CE2 or an
   IMET route with assigned VPN label to ASBR2 according to [RFC4364],
   [RFC4659] and [I-D.heitz-bess-evpn-option-b], ASBR2 continues to
   assigns new label for the route and advertises it to ASBR1.  When
   ASBR1 receives the UPDATE and continues to advertise the route to
   PE1, ASBR1 should assign an SRv6 VPN service SID for it.  The SID
   indicates the new execution function (e.g., END.RM, it indicates that
   MPLS should replace the SRH) for exchanging the packet header from
   SRH to MPLS list.  The new function format is like the defination in
   [I-D.ietf-spring-srv6-network-programming] section 4.

   When a data flow packet, which has the destination to CE2, is
   received by ASBR1, ASBR1 recognizes the SRv6 SID, removes the outer
   IPv6 header and SRH, then adds a or a list of MPLS label in the
   packet, and forwards it to PE2.  Note that the label stack is needed
   when the packet continues to enter an outer MPLS tunnel from ingress
   ASBR2 to egress PE2, otherwise only a single VPN label is
   encapsulated and the outer tunnel maybe a directly connected link.




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   Note that an END.RM SID may have non-zero argument length.  When the
   SRv6 SID's argument length is not zero, the value of the argument
   part is translated into an extra-label in the list.  for example, the
   extra-label is an ESI-label in IMET route cases.

4.  IANA Considerations

   IANA is requested to allocate a new code points for the new SRv6
   Endpoint Behaviors defined in this document.

                  +------+-------------+---------------+
                  | Type | Description | Reference     |
                  +------+-------------+---------------+
                  | TBD1 | END.RM      | This Document |
                  +------+-------------+---------------+

                                  Table 1

5.  Security Considerations

   This document introduces no new security consideration beyond those
   already specified in [RFC4364], [I-D.ietf-idr-bgp-prefix-sid],
   [I-D.ietf-spring-srv6-network-programming],
   [I-D.ietf-bess-srv6-services] and
   [I-D.agrawal-spring-srv6-mpls-interworking].

6.  References

6.1.  Normative References

   [I-D.heitz-bess-evpn-option-b]
              Heitz, J., Sajassi, A., Drake, J., and J. Rabadan, "Multi-
              homing and E-Tree in EVPN with Inter-AS Option B", draft-
              heitz-bess-evpn-option-b-01 (work in progress), November
              2017.

   [I-D.ietf-bess-srv6-services]
              Dawra, G., Filsfils, C., Raszuk, R., Decraene, B., Zhuang,
              S., and J. Rabadan, "SRv6 BGP based Overlay services",
              draft-ietf-bess-srv6-services-04 (work in progress), July
              2020.

   [I-D.ietf-idr-bgp-prefix-sid]
              Previdi, S., Filsfils, C., Lindem, A., Sreekantiah, A.,
              and H. Gredler, "Segment Routing Prefix SID extensions for
              BGP", draft-ietf-idr-bgp-prefix-sid-27 (work in progress),
              June 2018.




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   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-17 (work in
              progress), August 2020.

   [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>.

   [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>.

   [RFC4659]  De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
              "BGP-MPLS IP Virtual Private Network (VPN) Extension for
              IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006,
              <https://www.rfc-editor.org/info/rfc4659>.

   [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>.

6.2.  Informative References

   [I-D.agrawal-spring-srv6-mpls-interworking]
              Agrawal, S., Ali, Z., Filsfils, C., Voyer, D., Dawra, G.,
              and Z. Li, "SRv6 and MPLS interworking", draft-agrawal-
              spring-srv6-mpls-interworking-02 (work in progress),
              February 2020.

Authors' Addresses

   Zheng Zhang
   ZTE Corporation

   Email: zhang.zheng@zte.com.cn


   Shaofu Peng
   ZTE Corporation

   Email: peng.shaofu@zte.com.cn







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   Greg Mirsky
   ZTE Corporation

   Email: gregimirsky@gmail.com


   Yubao Wang
   ZTE Corporation

   Email: wang.yubao2@zte.com.cn









































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