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Versions: (draft-dawra-bgp-srv6-vpn) 00 01 02 03 04 05 draft-dawra-bess-srv6-services

Inter-Domain Routing
Internet-Draft
Intended status: Standards Track                           G. Dawra, Ed.
Expires: April 25, 2019                                         LinkedIn
                                                             C. Filsfils
                                                                D. Dukes
                                                            P. Brissette
                                                             P. Camarilo
                                                           Cisco Systems
                                                                J. Leddy
                                                                 Comcast
                                                                D. Voyer
                                                              D. Bernier
                                                             Bell Canada
                                                            D. Steinberg
                                                    Steinberg Consulting
                                                               R. Raszuk
                                                            Bloomberg LP
                                                             B. Decraene
                                                                  Orange
                                                           S. Matsushima
                                                                SoftBank
                                                               S. Zhuang
                                                     Huawei Technologies
                                                        October 22, 2018


                 BGP Signaling for SRv6 based Services.
                      draft-dawra-idr-srv6-vpn-05

Abstract

   This draft defines procedures and messages for BGP SRv6-based L3VPN
   and EVPN.  It builds on RFC4364 "BGP/MPLS IP Virtual Private Networks
   (VPNs)" and RFC7432 "BGP MPLS-Based Ethernet VPN" and provides a
   migration path from MPLS-based VPNs to SRv6 based VPNs.

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/.





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   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 April 25, 2019.

Copyright Notice

   Copyright (c) 2018 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 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  SRv6 Services TLV . . . . . . . . . . . . . . . . . . . . . .   4
   3.  BGP based L3 over SRv6  . . . . . . . . . . . . . . . . . . .   6
     3.1.  IPv4 VPN Over SRv6 Core . . . . . . . . . . . . . . . . .   7
     3.2.  IPv6 VPN Over SRv6 Core . . . . . . . . . . . . . . . . .   7
     3.3.  Global IPv4 over SRv6 Core  . . . . . . . . . . . . . . .   8
     3.4.  Global IPv6 over SRv6 Core  . . . . . . . . . . . . . . .   8
   4.  BGP based Ethernet VPN(EVPN) over SRv6  . . . . . . . . . . .   9
     4.1.  Ethernet Auto-discovery Route over SRv6 Core  . . . . . .  10
       4.1.1.  EVPN Route Type-1(Per ES AD)  . . . . . . . . . . . .  10
       4.1.2.  Prefix Type-1(Per EVI/ES AD)  . . . . . . . . . . . .  11
     4.2.  MAC/IP Advertisement Route(Type-2) with SRv6 Core . . . .  11
     4.3.  Inclusive Multicast Ethernet Tag Route with SRv6 Core . .  13
     4.4.  Ethernet Segment Route with SRv6 Core . . . . . . . . . .  14
     4.5.  IP prefix router(Type-5) with SRv6 Core . . . . . . . . .  15
     4.6.  Multicast routes (EVPN Route Type-6, Type-7, Type-8)  . .  15
   5.  Migration from L3 MPLS based Segment Routing to SRv6 Segment
       Routing . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  16
   7.  Error Handling of BGP SRv6 SID Updates  . . . . . . . . . . .  17
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   10. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . .  18
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18



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     11.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     11.2.  Informative References . . . . . . . . . . . . . . . . .  19
     11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  20
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . .  20
   Appendix B.  Contributors . . . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   SRv6 refers to Segment Routing instantiated on the IPv6 dataplane [I-
   D.filsfils-spring-srv6-network-programming][I-D.ietf-6man-segment-rou
   ting-header].

   SRv6 based BGP services refers to the L3 and L2 overlay services with
   BGP as control plane and SRv6 as dataplane.

   SRv6 SID refers to a SRv6 Segment Identifier as defined in
   [I-D.filsfils-spring-srv6-network-programming].

   SRv6 Service SID refers to an SRv6 SID that MAY be associated with
   one of the service specific behavior on the advertising PE, such as
   (but not limited to) in the case of L3VPN service, END.DT
   (crossconnect to a VRF) or END.DX (crossconnect to a nexthop)
   functions as defined
   in[I-D.filsfils-spring-srv6-network-programming].

   To provide SRv6 Service service with best-effort connectivity, the
   egress PE signals an SRv6 Service SID with the VPN route.  The
   ingress PE encapsulates the VPN packet in an outer IPv6 header where
   the destination address is the SRv6 Service SID provided by the
   egress PE.  The underlay between the PE's only need to support plain
   IPv6 forwarding [RFC2460].

   To provide SRv6 Service service in conjunction with an underlay SLA
   from the ingress PE to the egress PE, the egress PE colors the
   overlay VPN route with a color extended
   community[I-D.ietf-idr-segment-routing-te-policy].  The ingress PE
   encapsulates the VPN packet in an outer IPv6 header with an SRH that
   contains the SR policy associated with the related SLA followed by
   the SRv6 Service SID associated with the route.  The underlay nodes
   whose SRv6 SID's are part of the SRH must support SRv6 data plane.

   BGP is used to advertise the reachability of prefixes in a particular
   VPN from an egress Provider Edge (egress-PE) to ingress Provider Edge
   (ingress-PE) nodes.






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   This document describes how existing BGP messages between PEs may
   carry SRv6 Segment IDs (SIDs) as a means to interconnect PEs and form
   VPNs.

2.  SRv6 Services TLV

   The SRv6 Service TLVs are defined as two new TLVs for BGP Prefix SID
   Attribute [I-D.ietf-idr-bgp-prefix-sid], to achieve signaling of SRv6
   Service SID for L3 and L2 services.

   BGP Prefix SID Attribute[I-D.ietf-idr-bgp-prefix-sid]is referred as
   BGP SID Attribute in the rest of the document.

   When an egress-PE is capable of SRv6 data-plane, it SHOULD signal
   SRv6 Service SID TLV within the BGP SID Attribute attached to MP-BGP
   NLRI defined in [RFC4659][RFC5549][RFC7432].  [RFC4364]

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   TLV Type    |             Length            |   RESERVED    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //  SRv6 Service Information (variable)                        //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This document defines the following two new TLVs for BGP SID
   Attribute.

   - SRv6 L3 Service TLV.  Type code 5 (to be assigned by IANA as
   described in section 8).  This TLV encodes Service SID information
   for the SRv6 based L3 services.  It corresponds to the equivalent
   functionality provided by an MPLS Label when received with a Layer 3
   VPN route [RFC4364].  Some functions which MAY be encoded, but not
   limited to, are End.DX4, End.DT4, End.DX6, End.DT6, etc.

   - SRv6 L2 Service TLV.  Type code 6 (to be assigned by IANA as
   described in section 8).  This TLV encodes Service SID information
   for the SRv6 based L2 services.  It corresponds to the equivalent
   functionality provided by an MPLS Label1 for EVPN Route-Types as
   defined in [RFC7432].  Some functions which MAY be encoded, but not
   limited to, are End.DX2, End.DX2V, End.DT2U, End.DT2M etc.

   The "SRv6 Service Information" is encoded as an un-ordered list of
   sub-TLVs ("Type/Length/Value" blocks), as following:







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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Service       |                               |              //
    | information   |                               |              //
    | sub-TLV Type  |    sub-TLV Length             |   Value      //
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This document defines a sub-TLV Type code to encode a single SRv6 SID
   value along with its properties as following:

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |sub-TLV Type=1 |  sub-TLV Length               |   RESERVED1   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    //  SRv6 SID Value (16 bytes)                                  //
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | SID Flags     |  Endpoint Behavior            |   RESERVED2   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | SRv6 SID Optional Information                                 |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   o  Type is 1 (to be assigned by IANA as described in Section 8).  As
      defined to be "SID information sub-TLV".

   o  Length: 16 bit field.  The total length of the value portion of
      the sub-TLV.

   o  RESERVED1: 8 bit field.  SHOULD be 0 on transmission and MUST be
      ignored on reception.

   o  SRv6 SID Value: 128 bit field.  Encodes an SRv6 SID as defined in
      [I-D.filsfils-spring-srv6-network-programming]

   o  SID Flags: 8 bit field.  Encodes SRv6 SID Flags.  Value is opaque
      to BGP.

   o  Endpoint Behavior : 16 bit field.  Encodes Endpoint behavior.  For
      SRv6 VPN services, this field is always set to (0xFFFF).

   o  RESERVED2: 8 bit field.  SHOULD be 0 on transmission and MUST be
      ignored on reception.

   o  SRv6 SID Optional Information.  Variable length.  Encodes optional
      properties as described below.



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   SRv6 SID Optional information is encoded as a list of "SID optional
   information sub-TLV" blocks.  Where each block is encoded as
   Type/Length/Value triplet.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | SID Optional  |  sub-TLV Length               |   Value      //
       | information   |                               |              //
       | sub-TLV Type  |                               |              //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   No Type codes for SID Optional information sub-TLV are defined at
   this point.

3.  BGP based L3 over SRv6

   BGP egress nodes (egress-PEs) advertise a set of reachable prefixes.
   Standard BGP update propagation schemes [RFC4271], which MAY make use
   of route reflectors [RFC4456], are used to propagate these prefixes.
   BGP ingress nodes (ingress-PE) receive these advertisements and may
   add the prefix to the RIB in an appropriate VRF.

   Egress-PEs which supports SRv6-VPN advertises a Service SID encoded
   within SRv6 Service TLV within BGP SID attribute, with the VPN
   routes.  The Service SID thus signaled only has local significance at
   the egress-PE, where it is allocated or configured on a per-CE or
   per-VRF basis.  In practice, the SID encodes a cross-connect to a
   specific Address Family table (END.DT) or next-hop/interface (END.DX)
   as defined in the SRv6 Network Programming Document
   [I-D.filsfils-spring-srv6-network-programming].

   The SRv6 Service SID MAY be routable within the AS of the egress-PE
   and serves the dual purpose of providing reachability between
   ingress-PE and egress-PE while also encoding the VPN identifier.

   To support SRv6 based L3VPN overlay, a SID is advertised with BGP
   MPLS L3VPN route update[RFC4364].  SID is encoded in a SRv6 Service
   SID TLV within the optional transitive BGP SID
   attribute[I-D.ietf-idr-bgp-prefix-sid].  This attribute serves two
   purposes; first it indicates that the BGP egress device is reachable
   via an SRv6 underlay and the BGP ingress device receiving this route
   MAY choose to encapsulate or insert an SRv6 SRH, second it indicates
   the value of the SID to include in the SRH encapsulation.  For L3VPN,
   only a single SRv6 Service SID MAY be necessary.  A BGP speaker
   supporting an SRv6 underlay MAY distribute SID per route via the SRv6
   Service TLV.  If the BGP speaker supports MPLS based L3VPN
   simultaneously, it MAY also populate the Label values in L3VPN route



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   NLRI, and allow the BGP ingress device to decide which encapsulation
   to use.  If the BGP speaker does not support MPLS based L3VPN
   services the MPLS Labels in L3VPN NLRI MUST be set to IMPLICIT-
   NULL.[RFC7432]

   At an ingress-PE, BGP installs the advertised prefix in the correct
   RIB table, recursive via an SR Policy leveraging the received SRv6
   Service SID.

   Assuming best-effort connectivity to the egress PE, the SR policy has
   a path with a SID list made up of a single SID: the SRv6 Service SID
   received with the related BGP route update.

   However, when VPN route is colored with an extended color community C
   and signaled with Next-Hop N and the ingress PE has a valid SRv6
   Policy (N, C) associated with SID list <S1,S2, S3>
   [I-D.filsfils-spring-segment-routing-policy] then the SR Policy is
   <S1, S2, S3, SRv6 Service SID>.

   Multiple VPN routes MAY resolve recursively on the same SR Policy.

3.1.  IPv4 VPN Over SRv6 Core

   IPv4 VPN Over IPv6 Core is defined in [RFC5549], the MP_REACH_NLRI is
   encoded as follows for an SRv6 Core:

   o  AFI = 1

   o  SAFI = 128

   o  Length of Next Hop Network Address = 16 (or 32)

   o  Network Address of Next Hop = IPv6 address of the egress PE

   o  NLRI = IPv4-VPN routes

   o  Label = Implicit-Null

   SRv6 Service SID is encoded as part of the SRv6 Service SID TLV
   defined in Section 2.  The function of the SRv6 SID is entirely up to
   the originator of the advertisement.  In practice, the function may
   likely be End.DX4 or End.DT4.

3.2.  IPv6 VPN Over SRv6 Core

   IPv6 VPN over IPv6 Core is defined in [RFC4659], the MP_REACH_NLRI is
   enclosed as follows for an SRv6 Core:




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   o  AFI = 2

   o  SAFI = 128

   o  Length of Next Hop Network Address = 16 (or 32)

   o  Network Address of Next Hop = IPv6 address of the egress PE

   o  NLRI = IPv6-VPN routes

   o  Label = Implicit-Null

   SRv6 Service SID are encoded as part of the SRv6 Service SID TLV
   defined in Section 2.  The function of the IPv6 SRv6 SID is entirely
   up to the originator of the advertisement.  In practice the function
   may likely be End.DX6 or End.DT6.

3.3.  Global IPv4 over SRv6 Core

   IPv4 over IPv6 Core is defined in [RFC5549].  The MP_REACH_NLRI is
   encoded with:

   o  AFI = 1

   o  SAFI = 1

   o  Length of Next Hop Network Address = 16 (or 32)

   o  Network Address of Next Hop = IPv6 address of Next Hop

   o  NLRI = IPv4 routes

   SRv6 SID for Global IPv4 routes is encoded as part of the SRv6
   Service SID defined in Section 2.  The function of the SRv6 SID is
   entirely up to the originator of the advertisement.  In practice, the
   function may likely be End.DX6 or End.DT6.

3.4.  Global IPv6 over SRv6 Core

   The MP_REACH_NLRI is encoded with:

   o  AFI = 2

   o  SAFI = 1

   o  Length of Next Hop Network Address = 16 (or 32)

   o  Network Address of Next Hop = IPv6 address of Next Hop



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   o  NLRI = IPv6 routes

   SRv6 SID for Global IPv6 routes is encoded as part of the SRv6
   Service SID defined in Section 2.  The function of the SRv6 SID is
   entirely up to the originator of the advertisement.  In practice, the
   function may likely be End.DX6 or End.DT6.

   Also, by utilizing the SRv6 Service SID TLV, as defined in Section 2,
   to encode the Global SID, BGP free core is possible by encapsulating
   all BGP traffic from edge to edge over SRv6.

4.  BGP based Ethernet VPN(EVPN) over SRv6

   Ethernet VPN(EVPN), as defined in [RFC7432] provides an extendable
   method of building an EVPN overlay.  It primarily focuses on MPLS
   based EVPNs but calls out the extensibility to IP based EVPN
   overlays.  It defines 4 route-types which carry prefixes and MPLS
   Label attributes, the Labels each have specific use for MPLS
   encapsulation of EVPN traffic.  The fifth route-type carrying MPLS
   label information (and thus encapsulation information) for EVPN is
   defined in[I-D.ietf-bess-evpn-prefix-advertisement].  The Route Types
   discussed below are:

   o  Ethernet Auto-discovery Route

   o  MAC/IP Advertisement Route

   o  Inclusive Multicast Ethernet Tag Route

   o  Ethernet Segment route

   o  IP prefix route

   o  Selective Multicast route

   o  IGMP join sync route

   o  IGMP leave sync route

   To support SRv6 based EVPN overlays a SRv6 Service SID is advertised
   in route-type 1,2,3 and 5 above.  The SRv6 Service SID (or list of
   those, when applicable) per route-type are advertised in SRv6 Service
   TLV, as described in section 2.  Signaling of SRv6 Service SID serves
   two purposes; first it indicates that the BGP egress device is
   reachable via an SRv6 underlay and the BGP ingress device receiving
   this route MAY choose to encapsulate or insert an SRv6 SRH, second it
   indicates the value of the SID or SIDs to include in the SRH
   encapsulation.  If the BGP speaker does not support MPLS based EVPN



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   services the MPLS Labels in EVPN route types MUST be set to IMPLICIT-
   NULL.

4.1.  Ethernet Auto-discovery Route over SRv6 Core

   Ethernet Auto-discovery (A-D) routes are Type-1 route type defined in
   [RFC7432]and may be used to achieve split horizon filtering, fast
   convergence and aliasing.  EVPN route type-1 is also used in EVPN-
   VPWS as well as in EVPN flexible cross-connect; mainly used to
   advertise point-to-point services id.

   Multi-homed PEs MAY advertise an Ethernet auto discovery route per
   Ethernet segment with the introduced ESI MPLS label extended
   community defined in [RFC7432].The extended community label is set to
   implicit-null.  PEs may identify other PEs connected to the same
   Ethernet segment after the EVPN type-4 ES route exchange.  All the
   multi-homed and remote PEs that are part of same EVI may import the
   auto discovery route.

   EVPN Route Type-1 is encoded as follows for SRv6 Core:

                   +---------------------------------------+
                   |  RD (8 octets)                        |
                   +---------------------------------------+
                   |Ethernet Segment Identifier (10 octets)|
                   +---------------------------------------+
                   |  Ethernet Tag ID (4 octets)           |
                   +---------------------------------------+
                   |  MPLS label (3 octets)                |
                   +---------------------------------------+

   For a SRv6 only BGP speaker for an SRv6 Core:

   o  SRv6 Service SID TLV MAY be advertised with the route.

4.1.1.  EVPN Route Type-1(Per ES AD)

   Where:

   o  BGP next-hop: IPv6 address of an egress PE

   o  Ethernet Tag ID: all FFFF's

   o  MPLS Label: always set to zero value

   o  Extended Community: Per ES AD, ESI label extended community





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   BGP SID Attribute with SRv6 Service TLV MAY be advertised along with
   the route advertisement and the behavior of the SRv6 Service SID thus
   signaled, is entirely up to the originator of the advertisement.
   This is typically used to signal Arg.FE2 SID argument for applicable
   End.DT2M SIDs.

4.1.2.  Prefix Type-1(Per EVI/ES AD)

   Where:

   o  BGP next-hop: IPv6 address of an egress PE

   o  Ethernet Tag ID: non-zero for VLAN aware bridging, EVPN VPWS and
      FXC

   o  MPLS Label: Implicit-Null

   BGP SID Attribute with SRv6 Service TLV MAY be advertised along with
   the route advertisement and the behavior of the SRv6 Service SID is
   entirely up to the originator of the advertisement.  In practice, the
   behavior would likely be END.DX2, END.DX2V or END.DT2U.

4.2.  MAC/IP Advertisement Route(Type-2) with SRv6 Core

   EVPN route type-2 is used to advertise unicast traffic MAC+IP address
   reachability through MP-BGP to all other PEs in a given EVPN
   instance.

   A MAC/IP Advertisement route type is encoded as follows for SRv6
   Core:





















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                   +---------------------------------------+
                   |  RD (8 octets)                        |
                   +---------------------------------------+
                   |Ethernet Segment Identifier (10 octets)|
                   +---------------------------------------+
                   |  Ethernet Tag ID (4 octets)           |
                   +---------------------------------------+
                   |  MAC Address Length (1 octet)         |
                   +---------------------------------------+
                   |  MAC Address (6 octets)               |
                   +---------------------------------------+
                   |  IP Address Length (1 octet)          |
                   +---------------------------------------+
                   |  IP Address (0, 4, or 16 octets)      |
                   +---------------------------------------+
                   |  MPLS Label1 (3 octets)               |
                   +---------------------------------------+
                   |  MPLS Label2 (0 or 3 octets)          |
                   +---------------------------------------+

   where:

   o  BGP next-hop: IPv6 address of an egress PE

   o  MPLS Label1: Implicit-null

   o  MPLS Label2: Implicit-null

   BGP SID Attribute with SRv6 Service TLV MAY be advertised.  The
   behavior of the SRv6 Service SID is entirely up to the originator of
   the advertisement.  In practice, the behavior of the SRv6 SID is as
   follows:

   o  END.DX2, END.DT2U (Layer 2 portion of the route)

   o  END.DT6/4 or END.DX6/4 (Layer 3 portion of the route)

   Described below are different types of Type-2 advertisements.

   o  MAC/IP Advertisement Route(Type-2) with MAC Only

      *  BGP next-hop: IPv6 address of egress PE

      *  MPLS Label1: Implicit-null

      *  MPLS Label2: Implicit-null





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      *  SRv6 Service SID TLV within BGP SID Attribute MAY encode
         END.DX2 or END.DT2U behavior

   o  MAC/IP Advertisement Route(Type-2) with MAC+IP

      *  BGP next-hop: IPv6 address of egress PE

      *  MPLS Label1: Implicit-Null

      *  MPLS Label2: Implicit-Null

      *  SRv6 Service TLV within BGP SID Attribute MAY encode Layer2
         END.DX2 or END.DT2U behavior and Layer3 END.DT6/4 or END.DX6/4
         behavior

4.3.  Inclusive Multicast Ethernet Tag Route with SRv6 Core

   EVPN route Type-3 is used to advertise multicast traffic reachability
   information through MP-BGP to all other PEs in a given EVPN instance.

                  +---------------------------------------+
                  |  RD (8 octets)                        |
                  +---------------------------------------+
                  |  Ethernet Tag ID (4 octets)           |
                  +---------------------------------------+
                  |  IP Address Length (1 octet)          |
                  +---------------------------------------+
                  |  Originating Router's IP Address      |
                  |          (4 or 16 octets)             |
                  +---------------------------------------+

   An Inclusive Multicast Ethernet Tag route type specific EVPN NLRI
   consists of the following [RFC7432] where:

   o  BGP next-hop: IPv6 address of egress PE

   o  SRv6 Service TLV MAY encode END.DX2/END.DT2M function.

   o  BGP Attribute: PMSI Tunnel Attribute[RFC6514] MAY contain MPLS
      implicit-null label and Tunnel Type would be similar to defined in
      EVPN Type-6 i.e. Ingress replication route.

   The format of PMSI Tunnel Attribute attribute is encoded as follows
   for an SRv6 Core:







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                  +---------------------------------------+
                  |  Flag (1 octet)                       |
                  +---------------------------------------+
                  |  Tunnel Type (1 octet)                |
                  +---------------------------------------+
                  |  MPLS label (3 octet)                 |
                  +---------------------------------------+
                  |  Tunnel Identifier (variable)         |
                  +---------------------------------------+

   o  Flag: zero value defined per [RFC7432]

   o  Tunnel Type: defined per [RFC6514]

   o  MPLS label: Implicit-Null

   o  Tunnel Identifier: IP address of egress PE

   SRv6 Service TLV may be encoded as part of BGP SID Attribute.  The
   behavior of the SRv6 Service SID is entirely up to the originator of
   the advertisement.  In practice, the behavior of the SRv6 SID is as
   follows:

   o  END.DX2 or END.DT2M function

   o  The ESI Filtering argument(Arg.FE2) carried along with EVPN Route
      Type-1 (in SRv6 VPN SID), MAY be merged together with the
      applicable End.DT2M SID advertised by remote PE by doing a bitwise
      logical OR to create a single SID on the ingress PE for Split-
      horizon and other filtering mechanisms.  Details of filtering
      mechanisms are described in[RFC7432]

4.4.  Ethernet Segment Route with SRv6 Core

   An Ethernet Segment route type specific EVPN NLRI consists of the
   following defined in [RFC7432]

                  +---------------------------------------+
                  |  RD (8 octets)                        |
                  +---------------------------------------+
                  |  Ethernet Tag ID (4 octets)           |
                  +---------------------------------------+
                  |  IP Address Length (1 octet)          |
                  +---------------------------------------+
                  |  Originating Router's IP Address      |
                  |          (4 or 16 octets)             |
                  +---------------------------------------+




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   where:

   o  BGP next-hop: IPv6 address of egress PE

   As opposed to the previous route types, SRv6 Service TLV as part of
   BGP SID Attribute, is NOT advertised along with the route.  The
   processing of that route has not changed; it remains as described in
   [RFC7432].

4.5.  IP prefix router(Type-5) with SRv6 Core

   EVPN route Type-5 is used to advertise IP address reachability
   through MP-BGP to all other PEs in a given EVPN instance.  IP address
   may include host IP prefix or any specific subnet.  EVPN route Type-5
   is defined in[I-D.ietf-bess-evpn-prefix-advertisement]

   An IP Prefix advertisement is encoded as follows for an SRv6 Core:

                  +---------------------------------------+
                  |  RD (8 octets)                        |
                  +---------------------------------------+
                  |Ethernet Segment Identifier (10 octets)|
                  +---------------------------------------+
                  |  Ethernet Tag ID (4 octets)           |
                  +---------------------------------------+
                  |  IP Prefix Length (1 octet)           |
                  +---------------------------------------+
                  |  IP Prefix (4 or 16 octets)           |
                  +---------------------------------------+
                  |  GW IP Address (4 or 16 octets)       |
                  +---------------------------------------+
                  |  MPLS Label (3 octets)                |
                  +---------------------------------------+

   o  BGP next-hop: IPv6 address of egress PE

   o  MPLS Label: Implicit-Null

   BGP SID Attribute with SRv6 Service TLV MAY be advertised.  The
   behavior of the SRv6 Service SID is entirely up to the originator of
   the advertisement.  In practice, the behavior of the SRv6 SID is an
   End.DT6/4 or End.DX6/4.

4.6.  Multicast routes (EVPN Route Type-6, Type-7, Type-8)

   These routes do not require any additional SRv6 Service TLV.  As per
   EVPN route-type 4, the BGP nexthop is equal to the IPv6 address of




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   egress PE.  More details may be added in future revisions of this
   document.

5.  Migration from L3 MPLS based Segment Routing to SRv6 Segment Routing

   Migration from IPv4 to IPv6 is independent of SRv6 BGP endpoints, and
   the selection of which route to use (received via the IPv4 or IPv6
   session) is a local configurable decision of the ingress-PE, and is
   outside the scope of this document.

   Migration from IPv6 MPLS based underlay to an SRv6 underlay with BGP
   speakers is achieved with a few simple rules at each BGP speaker.

At Egress-PE
  If BGP offers an SRv6 Service service
      Then BGP allocates an SRv6 Service SID for the VPN service
      and adds the BGP SRv6 Service SID TLV while advertising VPN prefixes.
  If BGP offers an MPLS VPN service
      Then BGP allocates an MPLS Label for the VPN service and
      use it in NLRI as normal for MPLS L3 VPNs.
  else MPLS label for VPN service is set to IMPLICIT-NULL.

At Ingress-PE
  *Selection of which encapsulation below (SRv6 Service or MPLS-VPN) is
   defined by local BGP policy
  If BGP supports SRv6 Service service, and
  receives a BGP SID Attribute with an SRv6 Service TLV encoding a SRv6 Service SID
      Then BGP programs the destination prefix in RIB recursive via
      the related SR Policy.
  If BGP supports MPLS VPN service, and
  the MPLS Label is not Implicit-Null
      Then the MPLS label is used as a VPN label and inserted with the
      prefix into RIB via the BGP Nexthop.


6.  Implementation Status

   The SRv6 Service is available for SRv6 on various Cisco hardware and
   other software platforms.  An end-to-end integration of SRv6 L3VPN,
   SRv6 Traffic-Engineering and Service Chaining.  All of that with
   data-plane interoperability across different implementations [1]:

   o  Three Cisco Hardware-forwarding platforms: ASR 1K, ASR 9k and NCS
      5500

   o  Huawei network operating system

   o  Two Cisco network operating systems: IOS XE and IOS XR



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   o  Barefoot Networks Tofino on OCP Wedge-100BF

   o  Linux Kernel officially upstreamed in 4.10

   o  Fd.io

7.  Error Handling of BGP SRv6 SID Updates

   If the SRv6 Service TLV within the received BGP SID Attribute is
   malformed, consider the entire BGP SID Attribute as malformed,
   discard it and not propagate it further to other peers i.e. use the
   -attribute discard- action specified in [RFC7606] an error MAY be
   logged for further analysis.

   The SRv6 Service TLV is not considered to be malformed in the
   following cases.  The rest of the BGP SID Attribute MUST be processed
   normally.  An error MAY be logged for further analysis.

   o  The Service Information sub-TLV Type is unrecognized: all
      unrecognized sub-TLV Types must be stored locally and propagated
      further to other peers.  It is a matter of local implementation
      whether to use locally any recognized SID Types that may be
      present in the TLV along with the unrecognized Types.

   In addition, the following rules apply for processing NLRIs received
   with BGP SID Attribute containing SRv6 Service TLV:

   o  If the TLV is advertised by a CE peer, the receiving PE may
      discard it before advertising the route to its PE peers.

   o  If the received NLRI has neither a valid SRv6 Service SID nor a
      valid MPLS label as specified in [RFC4659][RFC5549][RFC7432] , the
      NLRI MUST be considered unreachable i.e. apply the -treat as
      withdraw- action specified in [RFC7606].

8.  IANA Considerations

   This document defines a new TLV, SRv6 Service TLV, within BGP SID
   attribute.  This document defines the following new TLV Types of BGP
   SID attribute:

   o  Type 5: SRv6 Layer3 Service

   o  Type 6: SRv6 Layer2 Service

   and are assigned to SRv6 Layer3 Service TLV and SRv6 Layer2 Service
   TLV defined in this document.




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   Further, this document defines a new sub-TLV; namely Service
   information sub-TLV, within SRv6 Service TLV, as described in
   Section 2.  A new registry "BGP SRv6 Service Information sub-TLV
   Types" is required and a new Type code point with value 1, is
   requested in this registry, to denote "SID information sub-TLV".

   Further, this document defines new optional sub-TLVs, namely "SID
   optional information sub-TLV" within Service information sub-TLV, as
   described in Section 2.  New registry for this purpose is required.

9.  Security Considerations

   This document introduces no new security considerations beyond those
   already specified in [RFC4271] and [RFC8277].

10.  Conclusions

   This document proposes extensions to the BGP to allow advertising
   certain attributes and functionalities related to SRv6.

11.  References

11.1.  Normative References

   [I-D.filsfils-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Hegde, S.,
              daniel.voyer@bell.ca, d., Lin, S., bogdanov@google.com,
              b., Krol, P., Horneffer, M., Steinberg, D., Decraene, B.,
              Litkowski, S., Mattes, P., Ali, Z., Talaulikar, K., Liste,
              J., Clad, F., and K. Raza, "Segment Routing Policy
              Architecture", draft-filsfils-spring-segment-routing-
              policy-06 (work in progress), May 2018.

   [I-D.filsfils-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-filsfils-spring-srv6-network-
              programming-05 (work in progress), July 2018.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
              d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-14 (work in
              progress), June 2018.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.



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   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <https://www.rfc-editor.org/info/rfc4456>.

   [RFC6514]  Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
              Encodings and Procedures for Multicast in MPLS/BGP IP
              VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
              <https://www.rfc-editor.org/info/rfc6514>.

   [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>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

   [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>.

11.2.  Informative References

   [I-D.ietf-bess-evpn-prefix-advertisement]
              Rabadan, J., Henderickx, W., Drake, J., Lin, W., and A.
              Sajassi, "IP Prefix Advertisement in EVPN", draft-ietf-
              bess-evpn-prefix-advertisement-11 (work in progress), May
              2018.

   [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.

   [I-D.ietf-idr-segment-routing-te-policy]
              Previdi, S., Filsfils, C., Jain, D., Mattes, P., Rosen,
              E., and S. Lin, "Advertising Segment Routing Policies in
              BGP", draft-ietf-idr-segment-routing-te-policy-04 (work in
              progress), July 2018.








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   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
              "IS-IS Extensions for Segment Routing", draft-ietf-isis-
              segment-routing-extensions-19 (work in progress), July
              2018.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.

   [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>.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.

   [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>.

   [RFC5549]  Le Faucheur, F. and E. Rosen, "Advertising IPv4 Network
              Layer Reachability Information with an IPv6 Next Hop",
              RFC 5549, DOI 10.17487/RFC5549, May 2009,
              <https://www.rfc-editor.org/info/rfc5549>.

11.3.  URIs

   [1] http://www.segment-routing.net

Appendix A.  Acknowledgements

   The authors would like to thank Shyam Sethuram for comments and
   discussion of TLV processing and validation.






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Appendix B.  Contributors

   Bart Peirens
   Proximus
   Belgium

   Email: bart.peirens@proximus.com

Authors' Addresses


   Gaurav Dawra (editor)
   LinkedIn
   USA

   Email: gdawra.ietf@gmail.com


   Clarence Filsfils
   Cisco Systems
   Belgium

   Email: cfilsfil@cisco.com


   Darren Dukes
   Cisco Systems
   Canada

   Email: ddukes@cisco.com


   Patrice Brissette
   Cisco Systems
   Canada

   Email: pbrisset@cisco.com


   Pablo Camarilo
   Cisco Systems
   Spain

   Email: pcamaril@cisco.com







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   Jonn Leddy
   Comcast
   USA

   Email: john_leddy@cable.comcast.com


   Daniel Voyer
   Bell Canada
   Canada

   Email: daniel.voyer@bell.ca


   Daniel Bernier
   Bell Canada
   Canada

   Email: daniel.bernier@bell.ca


   Dirk Steinberg
   Steinberg Consulting
   Germany

   Email: dws@steinberg.net


   Robert Raszuk
   Bloomberg LP
   USA

   Email: robert@raszuk.net


   Bruno Decraene
   Orange
   France

   Email: bruno.decraene@orange.com


   Satoru Matsushima
   SoftBank
   1-9-1,Higashi-Shimbashi,Minato-Ku
   Japan 105-7322

   Email: satoru.matsushima@g.softbank.co.jp



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   Shunwan Zhuang
   Huawei Technologies
   China

   Email: zhuangshunwan@huawei.com














































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