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SPRING                                                       C. Filsfils
Internet-Draft                                         P. Camarillo, Ed.
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: August 18, 2019                                        J. Leddy
                                                                 Comcast
                                                                D. Voyer
                                                             Bell Canada
                                                           S. Matsushima
                                                                SoftBank
                                                                   Z. Li
                                                     Huawei Technologies
                                                       February 14, 2019


                        SRv6 Network Programming
           draft-filsfils-spring-srv6-network-programming-07

Abstract

   This document describes the SRv6 network programming concept and its
   most basic functions.

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.

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 August 18, 2019.





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Copyright Notice

   Copyright (c) 2019 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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  SRv6 Segment  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Functions associated with a SID . . . . . . . . . . . . . . .   7
     4.1.  End: Endpoint . . . . . . . . . . . . . . . . . . . . . .   8
     4.2.  End.X: Layer-3 cross-connect  . . . . . . . . . . . . . .   9
     4.3.  End.T: Specific IPv6 table lookup . . . . . . . . . . . .  10
     4.4.  End.DX2: Decapsulation and L2 cross-connect . . . . . . .  10
     4.5.  End.DX2V: Decapsulation and VLAN L2 table lookup  . . . .  11
     4.6.  End.DT2U: Decapsulation and unicast MAC L2 table lookup .  12
     4.7.  End.DT2M: Decapsulation and L2 table flooding . . . . . .  12
     4.8.  End.DX6: Decapsulation and IPv6 cross-connect . . . . . .  13
     4.9.  End.DX4: Decapsulation and IPv4 cross-connect . . . . . .  14
     4.10. End.DT6: Decapsulation and specific IPv6 table lookup . .  15
     4.11. End.DT4: Decapsulation and specific IPv4 table lookup . .  15
     4.12. End.DT46: Decapsulation and specific IP table lookup  . .  16
     4.13. End.B6.Insert: Endpoint bound to an SRv6 policy . . . . .  17
     4.14. End.B6.Insert.Red: [...] with reduced SRH insertion . . .  18
     4.15. End.B6.Encaps: Endpoint bound to an SRv6 policy w/ encaps  18
     4.16. End.B6.Encaps.Red: [...] with reduced SRH insertion . . .  19
     4.17. End.BM: Endpoint bound to an SR-MPLS policy . . . . . . .  19
     4.18. End.S: Endpoint in search of a target in table T  . . . .  20
     4.19. SR-aware application  . . . . . . . . . . . . . . . . . .  21
     4.20. Non SR-aware application  . . . . . . . . . . . . . . . .  21
     4.21. Flavours  . . . . . . . . . . . . . . . . . . . . . . . .  21
       4.21.1.  PSP: Penultimate Segment Pop of the SRH  . . . . . .  21
       4.21.2.  USP: Ultimate Segment Pop of the SRH . . . . . . . .  22
       4.21.3.  USD: Ultimate Segment Decapsulation  . . . . . . . .  23
   5.  Transit behaviors . . . . . . . . . . . . . . . . . . . . . .  24
     5.1.  T: Transit behavior . . . . . . . . . . . . . . . . . . .  24
     5.2.  T.Insert: Transit with insertion of an SRv6 Policy  . . .  24



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     5.3.  T.Insert.Red: Transit with reduced insertion  . . . . . .  25
     5.4.  T.Encaps: Transit with encapsulation in an SRv6 Policy  .  25
     5.5.  T.Encaps.Red: Transit with reduced encapsulation  . . . .  26
     5.6.  T.Encaps.L2: Transit with encapsulation of L2 frames  . .  27
     5.7.  T.Encaps.L2.Red: Transit with reduced encaps of L2 frames  27
   6.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .  28
     6.1.  Counters  . . . . . . . . . . . . . . . . . . . . . . . .  28
     6.2.  Flow-based hash computation . . . . . . . . . . . . . . .  28
     6.3.  OAM . . . . . . . . . . . . . . . . . . . . . . . . . . .  28
   7.  Basic security for intra-domain deployment  . . . . . . . . .  29
     7.1.  SEC-1 . . . . . . . . . . . . . . . . . . . . . . . . . .  29
     7.2.  SEC-2 . . . . . . . . . . . . . . . . . . . . . . . . . .  30
     7.3.  SEC-3 . . . . . . . . . . . . . . . . . . . . . . . . . .  30
   8.  Control Plane . . . . . . . . . . . . . . . . . . . . . . . .  31
     8.1.  IGP . . . . . . . . . . . . . . . . . . . . . . . . . . .  31
     8.2.  BGP-LS  . . . . . . . . . . . . . . . . . . . . . . . . .  31
     8.3.  BGP IP/VPN/EVPN . . . . . . . . . . . . . . . . . . . . .  31
     8.4.  Summary . . . . . . . . . . . . . . . . . . . . . . . . .  32
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  33
   10. Work in progress  . . . . . . . . . . . . . . . . . . . . . .  36
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  36
   12. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  36
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  39
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  39
     13.2.  Informative References . . . . . . . . . . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction

   Segment Routing leverages the source routing paradigm.  An ingress
   node steers a packet through a ordered list of instructions, called
   segments.  Each one of these instructions represents a function to be
   called at a specific location in the network.  A function is locally
   defined on the node where it is executed and may range from simply
   moving forward in the segment list to any complex user-defined
   behavior.  The network programming consists in combining segment
   routing functions, both simple and complex, to achieve a networking
   objective that goes beyond mere packet routing.

   This document defines the SRv6 Network Programming concept and aims
   at standardizing the main segment routing functions to enable the
   creation of interoperable overlays with underlay optimization and
   service programming.

   The companion document
   [I-D.filsfils-spring-srv6-net-pgm-illustration] illustrates the
   concepts defined in this document.




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   Familiarity with the Segment Routing Header
   [I-D.ietf-6man-segment-routing-header] is assumed.

2.  Terminology

   SRH is the abbreviation for the Segment Routing Header.  We assume
   that the SRH may be present multiple times inside each packet.

   NH is the abbreviation of the IPv6 next-header field.

   NH=SRH means that the next-header field is 43 with routing type 4.

   When there are multiple SRHs, they must follow each other: the next-
   header field of all SRH, except the last one, must be SRH.

   The effective next-header (ENH) is the next-header field of the IP
   header when no SRH is present, or is the next-header field of the
   last SRH.

   In this version of the document, we assume that there are no other
   extension headers than the SRH.  These will be lifted in future
   versions of the document.

   SID: A Segment Identifier which represents a specific segment in
   segment routing domain.  The SID type used in this document is IPv6
   address (also referenced as SRv6 Segment or SRv6 SID).

   A SID list is represented as <S1, S2, S3> where S1 is the first SID
   to visit, S2 is the second SID to visit and S3 is the last SID to
   visit along the SR path.

   (SA,DA) (S3, S2, S1; SL) represents an IPv6 packet with:

   - IPv6 header with source address SA, destination addresses DA and
     SRH as next-header

   - SRH with SID list <S1, S2, S3> with SegmentsLeft = SL

   - Note the difference between the <> and () symbols: <S1, S2, S3>
     represents a SID list where S1 is the first SID and S3 is the last
     SID to traverse.  (S3, S2, S1; SL) represents the same SID list but
     encoded in the SRH format where the rightmost SID in the SRH is the
     first SID and the leftmost SID in the SRH is the last SID.  When
     referring to an SR policy in a high-level use-case, it is simpler
     to use the <S1, S2, S3> notation.  When referring to an
     illustration of the detailed packet behavior, the (S3, S2, S1; SL)
     notation is more convenient.




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   - The payload of the packet is omitted.

   SRH[SL] represents the SID pointed by the SL field in the first SRH.
   In our example, SRH[2] represents S1, SRH[1] represents S2 and SRH[0]
   represents S3.

   FIB is the abbreviation for the forwarding table.  A FIB lookup is a
   lookup in the forwarding table.

   When a packet is intercepted on a wire, it is possible that SRH[SL]
   is different from the DA.

3.  SRv6 Segment

   An SRv6 Segment is a 128-bit value.  "SID" (abbreviation for Segment
   Identifier) is often used as a shorter reference for "SRv6 Segment".

   An SRv6-capable node N maintains a "My SID Table".  This table
   contains all the SRv6 segments explicitly instantiated at node N.  N
   is the parent node for these SIDs.

   A local SID of N can be an IPv6 address associated to a local
   interface of N but it is not mandatory.  Nor is the "My SID table"
   populated by default with all IPv6 addresses defined on node N.

   In most use-cases, a local SID will NOT be an address associated to a
   local interface of N.

   A local SID of N could be routed to N but it does not have to be.
   Most often, it is routed to N via a shorter-mask prefix.


   Let's provide a classic illustration.

   Node N is configured with a loopback0 interface address of A:1::/32
   originated in its IGP.  Node N is configured with two SIDs: B:1:100::
   and B:2:101::.

   The entry A:1:: is not defined explicitly as an SRv6 SID and hence
   does not appear in the "My SID Table".  The entries B:1:100:: and
   B:2:101:: are defined explicitly as SRv6 SIDs and hence appear in the
   "My SID Table".

   The network learns about a path to B:1::/32 via the IGP and hence a
   packet destined to B:1:100:: would be routed up to N.  The network
   does not learn about a path to B:2::/32 via the IGP and hence a
   packet destined to B:2:101:: would not be routed up to N.




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   A packet could be steered to a non-routed SID B:2:101:: by using a
   SID list <...,B:1:100::,B:2:101::,...> where the non-routed SID is
   preceded by a routed SID to the same node.  This is similar to the
   local vs global segments in SR-MPLS.


   Every SRv6 SID instantiated has a specific instruction bound to it.
   This information is stored in the "My SID Table".  The "My SID Table"
   has three main purposes:

   - Define which SIDs are explicitly instantiated on that node

   - Specify which instruction is bound to each of the instantiated SIDs

   - Store the parameters associated with such instruction (i.e.  OIF,
     NextHop, VRF,...)

   We represent an SRv6 SID as LOC:FUNCT where LOC is the L most
   significant bits and FUNCT is the 128-L least significant bits.  L is
   called the locator length and is flexible.  Each operator is free to
   use the locator length it chooses.  Most often the LOC part of the
   SID is routable and leads to the node which instantiates that SID.

   The FUNCT part of the SID is an opaque identification of a local
   function bound to the SID.  The FUNCT value zero is invalid.

   Often, for simplicity of illustration, we will use a locator length
   of 32 bits.  This is just an example.  Implementations must not
   assume any a priori prefix length.

   A function may require additional arguments that would be placed
   immediately after the FUNCT.  In such case, the SRv6 SID will have
   the form LOC:FUNCT:ARGS::. For this reason, the "My SID Table"
   matches on a per longest-prefix-match basis.

   These arguments may vary on a per-packet basis and may contain
   information related to the flow, service, or any other information
   required by the function associated to the SRv6 SID.

   A node may receive a packet with an SRv6 SID in the DA without an
   SRH.  In such case the packet should still be processed by the
   Segment Routing engine.









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4.  Functions associated with a SID

   Each entry of the "My SID Table" indicates the function associated
   with the local SID and its parameters.

   We define hereafter a set of well-known functions that can be
   associated with a SID.

  End                Endpoint function
                     The SRv6 instantiation of a prefix SID
  End.X              Endpoint with Layer-3 cross-connect
                     The SRv6 instantiation of a Adj SID
  End.T              Endpoint with specific IPv6 table lookup
  End.DX2            Endpoint with decaps and L2 cross-connect
                     e.g. L2VPN use-case
  End.DX2V           Endpoint with decaps and VLAN L2 table lookup
                     EVPN Flexible cross-connect use-cases
  End.DT2U           Endpoint with decaps and unicast MAC L2table lookup
                     EVPN Bridging unicast use-cases
  End.DT2M           Endpoint with decaps and L2 table flooding
                     EVPN Bridging BUM use-cases with ESI filtering
  End.DX6            Endpoint with decaps and IPv6 cross-connect
                     e.g. IPv6-L3VPN (equivalent to per-CE VPN label)
  End.DX4            Endpoint with decaps and IPv4 cross-connect
                     e.g. IPv4-L3VPN (equivalent to per-CE VPN label)
  End.DT6            Endpoint with decaps and IPv6 table lookup
                     e.g. IPv6-L3VPN (equivalent to per-VRF VPN label)
  End.DT4            Endpoint with decaps and IPv4 table lookup
                     e.g. IPv4-L3VPN (equivalent to per-VRF VPN label)
  End.DT46           Endpoint with decaps and IP table lookup
                     e.g. IP-L3VPN (equivalent to per-VRF VPN label)
  End.B6.Insert      Endpoint bound to an SRv6 policy
                     SRv6 instantiation of a Binding SID
  End.B6.Insert.RED  [...] with reduced SRH insertion
                     SRv6 instantiation of a Binding SID
  End.B6.Encaps      Endpoint bound to an SRv6 policy with encaps
                     SRv6 instantiation of a Binding SID
  End.B6.Encaps.RED  [...] with reduced SRH insertion
                     SRv6 instantiation of a Binding SID
  End.BM             Endpoint bound to an SR-MPLS Policy
                     SRv6 instantiation of an SR-MPLS Binding SID
  End.S              Endpoint in search of a target in table T

   The list is not exhaustive.  In practice, any function can be
   attached to a local SID: e.g. a node N can bind a SID to a local VM
   or container which can apply any complex function on the packet.





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   We call N the node who has an explicitly instantiated SID S and we
   detail the function that N binds to S.

   At the end of this section we also present some flavours of these
   well-known functions.

4.1.  End: Endpoint

   The Endpoint function ("End" for short) is the most basic function.

   When N receives a packet whose IPv6 DA is S and S is a local End SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      decrement SL
 3.      update the IPv6 DA with SRH[SL]
 4.      FIB lookup on the updated DA                            ;; Ref1
 5.      forward accordingly to the matched entry                ;; Ref2
 6.   ELSE IF NH!=SRH
 7.      Send an ICMP parameter problem message; drop the packet ;; Ref3
 8.   ELSE
 9.      drop the packet

   Ref1: The End function performs the FIB lookup in the forwarding
   table associated to the ingress interface

   Ref2: If the FIB lookup matches a multicast state, then the related
   RPF check must be considered successful

   Ref3: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   A local SID could be bound to a function which authorizes the
   decapsulation of an outer header (e.g.  IPinIP) or the punting of the
   packet to TCP, UDP or any other protocol.  This however needs to be
   explicitly defined in the function bound to the local SID.  By
   default, a local SID bound to the well-known function "End"neither
   allows the decapsulation of an outer header nor the cleanup of an
   SRH.  As a consequence, an End SID cannot be the last SID of an SRH
   and cannot be the DA of a packet without SRH.

   This is the SRv6 instantiation of a Prefix SID
   [I-D.ietf-spring-segment-routing].








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4.2.  End.X: Layer-3 cross-connect

   The "Endpoint with cross-connect to an array of layer-3 adjacencies"
   function (End.X for short) is a variant of the End function.

   When N receives a packet destined to S and S is a local End.X SID, N
   does:

 1.   IF NH=SRH and SL > 0
 2.      decrement SL
 3.      update the IPv6 DA with SRH[SL]
 4.      forward to layer-3 adjacency bound to the SID S         ;; Ref1
 6.   ELSE IF NH!=SRH
 7.      Send an ICMP parameter problem message; drop the packet ;; Ref2
 8.   ELSE
 9.      drop the packet

   Ref1: If an array of adjacencies is bound to the End.X SID, then one
   entry of the array is selected based on a hash of the packet's
   header.

   Ref2: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   The End.X function is required to express any traffic-engineering
   policy.

   This is the SRv6 instantiation of an Adjacency SID
   [I-D.ietf-spring-segment-routing].

   If a node N has 30 outgoing interfaces to 30 neighbors, usually the
   operator would explicitly instantiate 30 End.X SIDs at N: one per
   layer-3 adjacency to a neighbor.  Potentially, more End.X could be
   explicitly defined (groups of layer-3 adjacencies to the same
   neighbor or to different neighbors).

   Note that with SR-MPLS, an AdjSID is typically preceded by a
   PrefixSID.  This is unlikely in SRv6 as most likely an End.X SID is
   globally routed to N.

   Note that if N has an outgoing interface bundle I to a neighbor Q
   made of 10 member links, N may allocate up to 11 End.X local SIDs for
   that bundle: one for the bundle itself and then up to one for each
   member link.  This is the equivalent of the L2-Link Adj SID in SR-
   MPLS [I-D.ietf-isis-l2bundles].






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4.3.  End.T: Specific IPv6 table lookup

   The "Endpoint with specific IPv6 table lookup" function (End.T for
   short) is a variant of the End function.

   When N receives a packet destined to S and S is a local End.T SID, N
   does:

 1.   IF NH=SRH and SL > 0                                       ;; Ref1
 2.      decrement SL
 3.      update the IPv6 DA with SRH[SL]
 4.      lookup the next segment in IPv6 table T associated with the SID
 5.      forward via the matched table entry
 6.   ELSE IF NH!=SRH
 7.      Send an ICMP parameter problem message; drop the packet ;; Ref2
 8.   ELSE
 9.      drop the packet

   Ref1: The End.T SID must not be the last SID

   Ref2: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   The End.T is used for multi-table operation in the core.

4.4.  End.DX2: Decapsulation and L2 cross-connect

   The "Endpoint with decapsulation and Layer-2 cross-connect to OIF"
   function (End.DX2 for short) is a variant of the endpoint function.

   When N receives a packet destined to S and S is a local End.DX2 SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH=59                                             ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 5.      forward the resulting frame to OIF bound to the SID S
 6.   ELSE
 7.      Send an ICMP parameter problem message                  ;; Ref3
 8.      drop the packet

   Ref1: An End.DX2 SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: We conveniently reuse the next-header value 59 allocated to
   IPv6 No Next Header [RFC8200].  When the SID corresponds to function




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   End.DX2 and the Next-Header value is 59, we know that an Ethernet
   frame is in the payload without any further header.

   Ref3: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   An End.DX2 function could be customized to expect a specific VLAN
   format and rewrite the egress VLAN header before forwarding on the
   outgoing interface.

   One of the applications of the End.DX2 function is the L2VPN/EVPN
   VPWS use-case.

4.5.  End.DX2V: Decapsulation and VLAN L2 table lookup

   The "Endpoint with decapsulation and specific VLAN table lookup"
   function (End.DX2V for short) is a variant of the endpoint function.

   When N receives a packet destined to S and S is a local End.DX2V SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH  = 59                                          ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 5.      lookup the exposed inner VLANs in L2 table T
 6.      forward via the matched table entry
 7.   ELSE
 8.      Send an ICMP parameter problem message                  ;; Ref3
 9.      drop the packet

   Ref1: An End.DX2V SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: We conveniently reuse the next-header value 59 allocated to
   IPv6 No Next Header [RFC8200].  When the SID corresponds to function
   End.DX2V and the Next-Header value is 59, we know that an Ethernet
   frame is in the payload without any further header.

   Ref3: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   An End.DX2V function could be customized to expect a specific VLAN
   format and rewrite the egress VLAN header before forwarding on the
   outgoing interface.

   The End.DX2V is used for EVPN Flexible cross-connect use-cases.




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4.6.  End.DT2U: Decapsulation and unicast MAC L2 table lookup

   The "Endpoint with decapsulation and specific unicast MAC L2 table
   lookup" function (End.DT2U for short) is a variant of the endpoint
   function.

   When N receives a packet destined to S and S is a local End.DT2U SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH  = 59                                          ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 5.      learn the exposed inner MAC SA in L2 table T            ;; Ref3
 6.      lookup the exposed inner MAC DA in L2 table T
 7.      IF matched entry in table T
 8.         forward via the matched table T entry
 9.      ELSE
10.         forward via all L2OIF entries in table T
11.   ELSE
12.      Send an ICMP parameter problem message                  ;; Ref4
13.      drop the packet

   Ref1: An End.DT2U SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: We conveniently reuse the next-header value 59 allocated to
   IPv6 No Next Header [RFC8200].  When the SID corresponds to function
   End.DT2U and the Next-Header value is 59, we know that an Ethernet
   frame is in the payload without any further header.

   Ref3: In EVPN, the learning of the exposed inner MAC SA is done via
   control plane.

   Ref4: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   The End.DT2U is used for EVPN Bridging unicast use cases.

4.7.  End.DT2M: Decapsulation and L2 table flooding

   The "Endpoint with decapsulation and specific L2 table flooding"
   function (End.DT2M for short) is a variant of the endpoint function.

   This function may take an argument: "Arg.FE2".  It is an argument
   specific to EVPN ESI filtering.  It is used to exclude a specific OIF
   (or set of OIFs) from L2 table T flooding.




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   When N receives a packet destined to S and S is a local End.DT2M SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH  = 59                                          ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 3.      learn the exposed inner MAC SA in L2 table T            ;; Ref3
 4.      forward on all L2OIF excluding the one specified in Arg.FE2
 5.   ELSE
 6.      Send an ICMP parameter problem message                  ;; Ref4
 7.      drop the packet

   Ref1: An End.DT2M SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: We conveniently reuse the next-header value 59 allocated to
   IPv6 No Next Header [RFC8200].  When the SID corresponds to function
   End.DT2M and the Next-Header value is 59, we know that an Ethernet
   frame is in the payload without any further header.

   Ref3: In EVPN, the learning of the exposed inner MAC SA is done via
   control plane

   Ref4: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   The End.DT2M is used for EVPN Bridging BUM use-case with ESI
   filtering capability.

4.8.  End.DX6: Decapsulation and IPv6 cross-connect

   The "Endpoint with decapsulation and cross-connect to an array of
   IPv6 adjacencies" function (End.DX6 for short) is a variant of the
   End.X function.

   When N receives a packet destined to S and S is a local End.DX6 SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH = 41                                           ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 5.      forward to layer-3 adjacency bound to the SID S         ;; Ref3
 6.   ELSE
 7.      Send an ICMP parameter problem message                  ;; Ref4
 8.      drop the packet




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   Ref1: The End.DX6 SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: 41 refers to IPv6 encapsulation as defined by IANA allocation
   for Internet Protocol Numbers

   Ref3: Selected based on a hash of the packet's header (at least SA,
   DA, Flow Label)

   Ref4: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   One of the applications of the End.DX6 function is the L3VPNv6 use-
   case where a FIB lookup in a specific tenant table at the egress PE
   is not required.  This would be equivalent to the per-CE VPN label in
   MPLS [RFC4364].

4.9.  End.DX4: Decapsulation and IPv4 cross-connect

   The "Endpoint with decapsulation and cross-connect to an array of
   IPv4 adjacencies" function (End.DX4 for short) is a variant of the
   End.X functions.

   When N receives a packet destined to S and S is a local End.DX4 SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH  =  4                                          ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 5.      forward to layer-3 adjacency bound to the SID S         ;; Ref3
 6.   ELSE
 7.      Send an ICMP parameter problem message                  ;; Ref4
 8.      drop the packet

   Ref1: The End.DX4 SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: 4 refers to IPv4 encapsulation as defined by IANA allocation
   for Internet Protocol Numbers

   Ref3: Selected based on a hash of the packet's header (at least SA,
   DA, Flow Label)

   Ref4: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.





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   One of the applications of the End.DX4 function is the L3VPNv4 use-
   case where a FIB lookup in a specific tenant table at the egress PE
   is not required.  This would be equivalent to the per-CE VPN label in
   MPLS [RFC4364].

4.10.  End.DT6: Decapsulation and specific IPv6 table lookup

   The "Endpoint with decapsulation and specific IPv6 table lookup"
   function (End.DT6 for short) is a variant of the End function.

   When N receives a packet destined to S and S is a local End.DT6 SID,
   N does:

 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH = 41                                           ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 5.      lookup the exposed inner IPv6 DA in IPv6 table T
 6.      forward via the matched table entry
 7.   ELSE
 8.      Send an ICMP parameter problem message                  ;; Ref3
 9.      drop the packet

   Ref1: the End.DT6 SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: 41 refers to IPv6 encapsulation as defined by IANA allocation
   for Internet Protocol Numbers

   Ref3: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   One of the applications of the End.DT6 function is the L3VPNv6 use-
   case where a FIB lookup in a specific tenant table at the egress PE
   is required.  This would be equivalent to the per-VRF VPN label in
   MPLS[RFC4364].

   Note that an End.DT6 may be defined for the main IPv6 table in which
   case and End.DT6 supports the equivalent of an IPv6inIPv6 decaps
   (without VPN/tenant implication).

4.11.  End.DT4: Decapsulation and specific IPv4 table lookup

   The "Endpoint with decapsulation and specific IPv4 table lookup"
   function (End.DT4 for short) is a variant of the End function.

   When N receives a packet destined to S and S is a local End.DT4 SID,
   N does:



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 1.   IF NH=SRH and SL > 0
 2.      drop the packet                                         ;; Ref1
 3.   ELSE IF ENH = 4                                            ;; Ref2
 4.      pop the (outer) IPv6 header and its extension headers
 5.      lookup the exposed inner IPv4 DA in IPv4 table T
 6.      forward via the matched table entry
 7.   ELSE
 8.      Send an ICMP parameter problem message                  ;; Ref3
 9.      drop the packet

   Ref1: the End.DT4 SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: 4 refers to IPv4 encapsulation as defined by IANA allocation
   for Internet Protocol Numbers

   Ref3: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   One of the applications of the End.DT4 is the L3VPNv4 use-case where
   a FIB lookup in a specific tenant table at the egress PE is required.
   This would be equivalent to the per-VRF VPN label in MPLS[RFC4364].

   Note that an End.DT4 may be defined for the main IPv4 table in which
   case and End.DT4 supports the equivalent of an IPv4inIPv6 decaps
   (without VPN/tenant implication).

4.12.  End.DT46: Decapsulation and specific IP table lookup

   The "Endpoint with decapsulation and specific IP table lookup"
   function (End.DT46 for short) is a variant of the End.DT4 and End.DT6
   functions.

   When N receives a packet destined to S and S is a local End.DT46 SID,
   N does:
















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  1.   IF NH=SRH and SL > 0
  2.      drop the packet                                        ;; Ref1
  3.   ELSE IF ENH  =  4                                         ;; Ref2
  4.      pop the (outer) IPv6 header and its extension headers
  5.      lookup the exposed inner IPv4 DA in IPv4 table T
  6.      forward via the matched table entry
  7.   ELSE IF ENH = 41                                          ;; Ref2
  8.      pop the (outer) IPv6 header and its extension headers
  9.      lookup the exposed inner IPv6 DA in IPv6 table T
 10.      forward via the matched table entry
 11.   ELSE
 12.      Send an ICMP parameter problem message                 ;; Ref3
 13.      drop the packet

   Ref1: the End.DT46 SID must always be the last SID, or it can be the
   Destination Address of an IPv6 packet with no SRH header.

   Ref2: 4 and 41 refer to IPv4 and IPv6 encapsulation respectively as
   defined by IANA allocation for Internet Protocol Numbers

   Ref3: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   One of the applications of the End.DT46 is the L3VPN use-case where a
   FIB lookup in a specific IP tenant table at the egress PE is
   required.  This would be equivalent to the per-VRF VPN label in MPLS
   [RFC4364].

   Note that an End.DT46 may be defined for the main IP table in which
   case and End.DT46 supports the equivalent of an IPinIPv6 decaps
   (without VPN/tenant implication).

4.13.  End.B6.Insert: Endpoint bound to an SRv6 policy

   The "Endpoint bound to an SRv6 Policy" is a variant of the End
   function.

   When N receives a packet destined to S and S is a local End.B6.Insert
   SID, N does:












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 1.   IF NH=SRH and SL > 0                                       ;; Ref1
 2.      do not decrement SL nor update the IPv6 DA with SRH[SL]
 3.      insert a new SRH, in between the IPv6 header and the
            received SRH
 4.      set the IPv6 DA to the first segment of the SRv6 Policy
 5.      forward according to the first segment of the SRv6 Policy
 6.   ELSE
 7.      Send an ICMP parameter problem message                  ;; Ref2
 8.      drop the packet

   Ref1: An End.B6.Insert SID, by definition, is never the last SID.

   Ref2: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   Note: Instead of the term "insert", "push" may also be used.

   The End.B6.Insert function is required to express scalable traffic-
   engineering policies across multiple domains.  This is the SRv6
   instantiation of a Binding SID [I-D.ietf-spring-segment-routing].

4.14.  End.B6.Insert.Red: [...] with reduced SRH insertion

   This is an optimization of the End.B6.Insert function.

   End.B6.Insert.Red will reduce the size of the SRH by one segment by
   avoiding the insertion of the first SID in the pushed SRH.  In this
   way, the first segment is only introduced in the DA and the packet is
   forwarded according to it.

   Note that SL value is initially pointing to a non-existing segment in
   the SRH.

4.15.  End.B6.Encaps: Endpoint bound to an SRv6 policy w/ encaps

   This is a variation of the End.B6.Insert behavior where the SRv6
   Policy also includes an IPv6 Source Address A.

   When N receives a packet destined to S and S is a local End.B6.Encaps
   SID, N does:











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 1.  IF NH=SRH and SL > 0
 2.    decrement SL and update the IPv6 DA with SRH[SL]
 3.    push an outer IPv6 header with its own SRH
 4.    set the outer IPv6 SA to A
 5.    set the outer IPv6 DA to the first segment of the SRv6 Policy
 6.    set outer payload length, trafic class and flow label   ;; Ref1,2
 7.    update the Next-Header value                            ;; Ref1
 8.    decrement inner Hop Limit or TTL                        ;; Ref1
 9.    forward according to the first segment of the SRv6 Policy
10.  ELSE
11.    Send an ICMP parameter problem message                  ;; Ref3
12.    drop the packet

   Ref 1: As described in [RFC2473] (Generic Packet Tunneling in IPv6
   Specification)

   Ref 2: As described in [RFC6437] (IPv6 Flow Label Specification)

   Ref3: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   Instead of simply inserting an SRH with the policy (End.B6), this
   behavior also adds an outer IPv6 header.  The source address defined
   for the outer header does not have to be a local SID of the node.

   The SRH MAY be omitted when the SRv6 Policy only contains one segment
   and there is no need to use any flag, tag or TLV.

4.16.  End.B6.Encaps.Red: [...] with reduced SRH insertion

   This is an optimization of the End.B6.Encaps function.

   End.B6.Encaps.Red will reduce the size of the SRH by one segment by
   avoiding the insertion of the first SID in the outer SRH.  In this
   way, the first segment is only introduced in the DA and the packet is
   forwarded according to it.

   Note that SL value is initially pointing to a non-existing segment in
   the SRH.

   The SRH MAY be omitted when the SRv6 Policy only contains one segment
   and there is no need to use any flag, tag or TLV.

4.17.  End.BM: Endpoint bound to an SR-MPLS policy

   The "Endpoint bound to an SR-MPLS Policy" is a variant of the End.B6
   function.




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   When N receives a packet destined to S and S is a local End.BM SID, N
   does:

 1.   IF NH=SRH and SL > 0                                       ;; Ref1
 2.      decrement SL and update the IPv6 DA with SRH[SL]
 3.      push an MPLS label stack <L1, L2, L3> on the received packet
 4.      forward according to L1
 5.   ELSE
 6.      Send an ICMP parameter problem message                  ;; Ref2
 7.      drop the packet

   Ref1: an End.BM SID, by definition, is never the last SID.

   Ref2: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   The End.BM function is required to express scalable traffic-
   engineering policies across multiple domains where some domains
   support the MPLS instantiation of Segment Routing.

   This is an SRv6 instantiation of an SR-MPLS Binding SID
   [I-D.ietf-spring-segment-routing].

4.18.  End.S: Endpoint in search of a target in table T

   The "Endpoint in search of a target in Table T" function (End.S for
   short) is a variant of the End function.

   When N receives a packet destined to S and S is a local End.S SID, N
   does:

 1.   IF NH=SRH and SL = 0                                       ;; Ref1
 2.      Send an ICMP parameter problem message                  ;; Ref2
 3.      drop the packet
 4.   ELSE IF match(last SID) in specified table T
 5.      forward accordingly
 6.   ELSE
 7.      apply the End behavior

   Ref1: By definition, an End.S SID cannot be the last SID, as the last
   SID is the targeted object.

   Ref2: ICMP error is sent to the source address with error code (TBD
   by IANA) "SR Upper-layer Header Error" and pointer set to the NH.

   The End.S function is required in information-centric networking
   (ICN) use-cases where the last SID in the SRv6 SID list represents a
   targeted object.  If the identification of the object would require



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   more than 128 bits, then obvious customization of the End.S function
   may either use multiple SIDs or a TLV of the SR header to encode the
   searched object ID.

4.19.  SR-aware application

   Generally, any SR-aware application can be bound to an SRv6 SID.
   This application could represent anything from a small piece of code
   focused on topological/tenant function to a larger process focusing
   on higher-level applications (e.g. video compression, transcoding
   etc.).

   The ways in which an SR-aware application binds itself on a local SID
   depends on the operating system.  Let us consider an SR-aware
   application running on a Linux operating system.  A possible approach
   is to associate an SRv6 SID to a target (virtual) interface, so that
   packets with IP DA corresponding to the SID will be sent to the
   target interface.  In this approach, the SR-aware application can
   simply listen to all packets received on the interface.

   A different approach for the SR-aware app is to listen to packets
   received with a specific SRv6 SID as IPv6 DA on a given transport
   port (i.e. corresponding to a TCP or UDP socket).  In this case, the
   app can read the SRH information with a getsockopt Linux system call
   and can set the SRH information to be added to the outgoing packets
   with a setsocksopt system call.

4.20.  Non SR-aware application

   [I-D.xuclad-spring-sr-service-programming] defines a set of
   additional functions in order to enable non SR-aware applications to
   be associated with an SRv6 SID.

4.21.  Flavours

   We present the PSP and USP variants of the functions End, End.X and
   End.T.  For each of these functions these variants can be enabled or
   disabled either individually or together.

4.21.1.  PSP: Penultimate Segment Pop of the SRH

   After the instruction 'update the IPv6 DA with SRH[SL]' is executed,
   the following instructions must be added:

 1.   IF updated SL = 0 & PSP is TRUE
 2.      pop the top SRH                                         ;; Ref1





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   Ref1: The received SRH had SL=1.  When the last SID is written in the
   DA, the End, End.X and End.T functions with the PSP flavour pop the
   first (top-most) SRH.  Subsequent stacked SRH's may be present but
   are not processed as part of the function.

4.21.2.  USP: Ultimate Segment Pop of the SRH

   We insert at the beginning of the pseudo-code the following
   instructions:

 1.   IF NH=SRH & SL = 0 & USP=TRUE                              ;; Ref1
 2.      pop the top SRH
 3.      restart the function processing on the modified packet  ;; Ref2

   Ref1: The next header is an SRH header

   Ref2: Typically SL of the exposed SRH is > 0 and hence the restarting
   of the complete function would lead to decrement SL, update the IPv6
   DA with SRH[SL], FIB lookup on updated DA and forward accordingly to
   the matched entry.































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4.21.3.  USD: Ultimate Segment Decapsulation

   We insert at the beginning of the pseudo-code the following
   instructions:

 1.   IF (NH=41) or (NH = SRH and SL = 0 and NNH = 41)
 2.      pop the (outer) IPv6 header and its extension headers
 3.      lookup the exposed inner IP DA and forward              ;; Ref1
 4.      forward via the matched table entry

   Ref1: In case that the USD flavor is applied on an End.X function,
   the packet is forwarded to the layer-3 adjancency bound to SID S
   without any lookup.






































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5.  Transit behaviors

   We define hereafter the set of basic transit behaviors.  These
   behaviors are not bound to a SID and they correspond to source SR
   nodes or transit nodes [I-D.ietf-6man-segment-routing-header].

 T                Transit behavior
 T.Insert         Transit behavior with insertion of an SRv6 policy
 T.Insert.Red     Transit behavior with reduced insert of an SRv6 policy
 T.Encaps         Transit behavior with encapsulation in an SRv6 policy
 T.Encaps.Red     Transit behavior with reduced encaps in an SRv6 policy
 T.Encaps.L2      T.Encaps applied to received L2 frames
 T.Encaps.L2.Red  T.Encaps.Red applied to received L2 frames

   This list can be expanded in case any new functionality requires it.

5.1.  T: Transit behavior

   As per [RFC8200], if a node N receives a packet (A, S2)(S3, S2, S1;
   SL=2) and S2 is neither a local address nor a local SID of N then N
   forwards the packet without inspecting the SRH.

   This means that N treats the following two packets with the same
   performance:

   - (A, S2)

   - (A, S2)(S3, S2, S1; SL=2)

   A transit node does not need to count by default the amount of
   transit traffic with an SRH extension header.  This accounting might
   be enabled as an optional behavior.

   A transit node MUST include the outer flow label in its ECMP load-
   balancing hash [RFC6437].

5.2.  T.Insert: Transit with insertion of an SRv6 Policy

   Node N receives two packets P1=(A, B2) and P2=(A,B2)(B3, B2, B1;
   SL=1).  B2 is neither a local address nor SID of N.

   N steers the transit packets P1 and P2 into an SRv6 Policy with one
   SID list <S1, S2, S3>.

   The "T.Insert" transit insertion behavior is defined as follows:






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 1.   insert the SRH (B2, S3, S2, S1; SL=3)             ;; Ref1, Ref1bis
 2.   set the IPv6 DA = S1
 3.   forward along the shortest path to S1

   Ref1: The received IPv6 DA is placed as last SID of the inserted SRH.

   Ref1bis: The SRH is inserted before any other IPv6 Routing Extension
   Header.

   After the T.Insert behavior, P1 and P2 respectively look like:

   - (A, S1) (B2, S3, S2, S1; SL=3)

   - (A, S1) (B2, S3, S2, S1; SL=3) (B3, B2, B1; SL=1)

5.3.  T.Insert.Red: Transit with reduced insertion

   The T.Insert.Red behavior is an optimization of the T.Insert
   behavior.  It is defined as follows:

   1.   insert the SRH (B2, S3, S2; SL=3)
   2.   set the IPv6 DA = S1
   3.   forward along the shortest path to S1

   T.Insert.Red will reduce the size of the SRH by one segment by
   avoiding the insertion of the first SID in the pushed SRH.  In this
   way, the first segment is only introduced in the DA and the packet is
   forwarded according to it.

   Note that SL value is initially pointing to a non-existing segment in
   the SRH.

   After the T.Insert.Red behavior, P1 and P2 respectively look like:

   - (A, S1) (B2, S3, S2; SL=3)

   - (A, S1) (B2, S3, S2; SL=3) (B3, B2, B1; SL=1)

5.4.  T.Encaps: Transit with encapsulation in an SRv6 Policy

   Node N receives two packets P1=(A, B2) and P2=(A,B2)(B3, B2, B1;
   SL=1).  B2 is neither a local address nor SID of N.

   N steers the transit packets P1 and P2 into an SR Encapsulation
   Policy with a Source Address T and a Segment list <S1, S2, S3>.

   The T.Encaps transit encapsulation behavior is defined as follows:




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1.   push an IPv6 header with its own SRH (S3, S2, S1; SL=2)
2.   set outer IPv6 SA = T and outer IPv6 DA = S1
3.   set outer payload length, traffic class and flow label    ;; Ref1,2
4.   update the Next-Header value                              ;; Ref1
5.   decrement inner Hop Limit or TTL                          ;; Ref1
6.   forward along the shortest path to S1

   After the T.Encaps behavior, P1 and P2 respectively look like:

   - (T, S1) (S3, S2, S1; SL=2) (A, B2)

   - (T, S1) (S3, S2, S1; SL=2) (A, B2) (B3, B2, B1; SL=1)

   The T.Encaps behavior is valid for any kind of Layer-3 traffic.  This
   behavior is commonly used for L3VPN with IPv4 and IPv6 deployments.

   The SRH MAY be omitted when the SRv6 Policy only contains one segment
   and there is no need to use any flag, tag or TLV.

   Ref 1: As described in [RFC2473] (Generic Packet Tunneling in IPv6
   Specification)

   Ref 2: As described in [RFC6437] (IPv6 Flow Label Specification)

5.5.  T.Encaps.Red: Transit with reduced encapsulation

   The T.Encaps.Red behavior is an optimization of the T.Encaps
   behavior.  It is defined as follows:

 1.   push an IPv6 header with its own SRH (S3, S2; SL=2)
 2.   set outer IPv6 SA = T and outer IPv6 DA = S1
 3.   set outer payload length, traffic class and flow label   ;; Ref1,2
 4.   update the Next-Header value                             ;; Ref1
 5.   decrement inner Hop Limit or TTL                         ;; Ref1
 6.   forward along the shortest path to S1

   Ref 1: As described in [RFC2473] (Generic Packet Tunneling in IPv6
   Specification)

   Ref 2: As described in [RFC6437] (IPv6 Flow Label Specification)

   T.Encaps.Red will reduce the size of the SRH by one segment by
   avoiding the insertion of the first SID in the SRH of the pushed IPv6
   packet.  In this way, the first segment is only introduced in the DA
   and the packet is forwarded according to it.

   Note that SL value is initially pointing to a non-existing segment in
   the SRH.



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   After the T.Encaps.Red behavior, P1 and P2 respectively look like:

   - (T, S1) (S3, S2; SL=2) (A, B2)

   - (T, S1) (S3, S2; SL=2) (A, B2) (B3, B2, B1; SL=1)

   The SRH MAY be omitted when the SRv6 Policy only contains one segment
   and there is no need to use any flag, tag or TLV.

5.6.  T.Encaps.L2: Transit with encapsulation of L2 frames

   While T.Encaps encapsulates the received IP packet, T.Encaps.L2
   encapsulates the received L2 frame (i.e. the received ethernet header
   and its optional VLAN header is in the payload of the outer packet).

   If the outer header is pushed without SRH, then the DA must be a SID
   of type End.DX2, End.DX2V, End.DT2U or End.DT2M and the next-header
   must be 59 (IPv6 NoNextHeader).  The received Ethernet frame follows
   the IPv6 header and its extension headers.

   Else, if the outer header is pushed with an SRH, then the last SID of
   the SRH must be of type End.DX2, End.DX2V, End.DT2U or End.DT2M and
   the next-header of the SRH must be 59 (IPv6 NoNextHeader).  The
   received Ethernet frame follows the IPv6 header and its extension
   headers.

   The SRH MAY be omitted when the SRv6 Policy only contains one segment
   and there is no need to use any flag, tag or TLV.

5.7.  T.Encaps.L2.Red: Transit with reduced encaps of L2 frames

   The T.Encaps.L2.Red behavior is an optimization of the T.Encaps.L2
   behavior.

   T.Encaps.L2.Red will reduce the size of the SRH by one segment by
   avoiding the insertion of the first SID in the SRH of the pushed IPv6
   packet.  In this way, the first segment is only introduced in the DA
   and the packet is forwarded according to it.

   Note that SL value is initially pointing to a non-existing segment in
   the SRH.

   The SRH MAY be omitted when the SRv6 Policy only contains one segment
   and there is no need to use any flag, tag or TLV.







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6.  Operation

6.1.  Counters

   Any SRv6 capable node SHOULD implement the following set of combined
   counters (packets and bytes):

   - CNT-1: Per entry of the "My SID Table", traffic that matched that
     SID and was processed correctly.

   - CNT-2: Per SRv6 Policy, traffic steered into it and processed
     correctly.

   Furthermore, an SRv6 capable node maintains an aggregate counter
   CNT-3 tracking the IPv6 traffic that was received with a destination
   address matching a local interface address that is not a locally
   instantiated SID and the next-header is SRH with SL>0.  We remind
   that this traffic is dropped as an interface address is not a local
   SID by default.  A SID must be explicitly instantiated.

6.2.  Flow-based hash computation

   When a flow-based selection within a set needs to be performed, the
   source address, the destination address and the flow-label MUST be
   included in the flow-based hash.

   This occurs when the destination address is updated, a FIB lookup is
   performed and multiple ECMP paths exist to the updated destination
   address.

   This occurs when End.X, End.DX4, or End.DX6 are bound to an array of
   adjacencies.

   This occurs when the packet is steered in an SR policy whose selected
   path has multiple SID lists
   [I-D.filsfils-spring-segment-routing-policy].

6.3.  OAM

   [I-D.ali-spring-srv6-oam] defines the OAM behavior for SRv6.  This
   includes the definition of the SRH Flag 'O-bit', as well as
   additional OAM Endpoint functions.









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7.  Basic security for intra-domain deployment

   We use the following terminology:

      An internal node is a node part of the domain of trust.

      A border router is an internal node at the edge of the domain of
      trust.

      An external interface is an interface of a border router towards
      another domain.

      An internal interface is an interface entirely within the domain
      of trust.

      The internal address space is the IP address block dedicated to
      internal interfaces.

      An internal SID is a SID instantiated on an internal node.

      The internal SID space is the IP address block dedicated to
      internal SIDs.

      External traffic is traffic received from an external interface to
      the domain of trust.

      Internal traffic is traffic that originates and ends within the
      domain of trust.

   The purpose of this section is to document how a domain of trust can
   operate SRv6-based services for internal traffic while preventing any
   external traffic from accessing the internal SRv6-based services.

   It is expected that future documents will detail enhanced security
   mechanisms for SRv6 (e.g. how to allow external traffic to leverage
   internal SRv6 services).

7.1.  SEC-1

   An SRv6 router MUST support an ACL on the external interface that
   drops any traffic with SA or DA in the internal SID space.

   A provider would generally do this for its internal address space to
   prevent access to internal addresses and in order to prevent
   spoofing.  The technique is extended to the local SID space.

   The typical counters of an ACL are expected.




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7.2.  SEC-2

   An SRv6 router MUST support an ACL with the following behavior:

   1.   IF (DA == LocalSID) && (SA != internal address or SID space)
   2.      drop

   This prevents access to locally instantiated SIDs from outside the
   operator's infrastructure.  Note that this ACL may not be enabled in
   all cases.  For example, specific SIDs can be used to provide
   resources to devices that are outside of the operator's
   infrastructure.

   The typical counters of an ACL are expected.

7.3.  SEC-3

   As per the End definition, an SRv6 router MUST only implement the End
   behavior on a local IPv6 address if that address has been explicitly
   enabled as an SRv6 SID.

   This address may or may not be associated with an interface.  This
   address may or may not be routed.  The only thing that matters is
   that the local SID must be explicitly instantiated and explicitly
   bound to a function.

   Packets received with destination address representing a local
   interface that has not been enabled as an SRv6 SID MUST be dropped.























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8.  Control Plane

   In an SDN environment, one expects the controller to explicitly
   provision the SIDs and/or discover them as part of a service
   discovery function.  Applications residing on top of the controller
   could then discover the required SIDs and combine them to form a
   distributed network program.

   The concept of "SRv6 network programming" refers to the capability
   for an application to encode any complex program as a set of
   individual functions distributed through the network.  Some functions
   relate to underlay SLA, others to overlay/tenant, others to complex
   applications residing in VM and containers.

   The specification of the SRv6 control-plane is outside the scope of
   this document.

   We limit ourselves to a few important observations.

8.1.  IGP

   The End, End.T and End.X SIDs express topological functions and hence
   are expected to be signaled in the IGP together with the flavours
   PSP, USP and USD[I-D.bashandy-isis-srv6-extensions].

   The presence of SIDs in the IGP do not imply any routing semantics to
   the addresses represented by these SIDs.  The routing reachability to
   an IPv6 address is solely governed by the classic, non-SID-related,
   IGP information.  Routing is not governed neither influenced in any
   way by a SID advertisement in the IGP.

   These three SIDs provide important topological functions for the IGP
   to build FRR/TI-LFA solution and for TE processes relying on IGP LSDB
   to build SR policies.

8.2.  BGP-LS

   BGP-LS is expected to be the key service discovery protocol.  Every
   node is expected to advertise via BGP-LS its SRv6 capabilities (e.g.
   how many SIDs in can insert as part of an T.Insert behavior) and any
   locally instantiated SID [I-D.dawra-idr-bgpls-srv6-ext].

8.3.  BGP IP/VPN/EVPN

   The End.DX4, End.DX6, End.DT4, End.DT6, End.DT46, End.DX2, End.DX2V,
   End.DT2U and End.DT2M SIDs are expected to be signaled in BGP
   [I-D.dawra-idr-srv6-vpn].




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8.4.  Summary

   The following table summarizes which SIDs are signaled in which
   signaling protocol.

        +-----------------------+-----+--------+-----------------+
        |                       | IGP | BGP-LS | BGP IP/VPN/EVPN |
        +-----------------------+-----+--------+-----------------+
        | End   (PSP, USP, USD) |  X  |   X    |                 |
        | End.X (PSP, USP, USD) |  X  |   X    |                 |
        | End.T (PSP, USP, USD) |  X  |   X    |                 |
        | End.DX2               |     |   X    |        X        |
        | End.DX2V              |     |   X    |        X        |
        | End.DT2U              |     |   X    |        X        |
        | End.DT2M              |     |   X    |        X        |
        | End.DX6               |  X  |   X    |        X        |
        | End.DX4               |  X  |   X    |        X        |
        | End.DT6               |  X  |   X    |        X        |
        | End.DT4               |  X  |   X    |        X        |
        | End.DT46              |  X  |   X    |        X        |
        | End.B6.Insert         |     |   X    |                 |
        | End.B6.Insert.Red     |     |   X    |                 |
        | End.B6.Encaps         |     |   X    |                 |
        | End.B6.Encaps.Red     |     |   X    |                 |
        | End.B6.BM             |     |   X    |                 |
        | End.S                 |     |   X    |                 |
        +-----------------------+-----+--------+-----------------+

              Table 1: SRv6 locally instanted SIDs signaling

   The following table summarizes which transit capabilities are
   signaled in which signaling protocol.

           +-----------------+-----+--------+-----------------+
           |                 | IGP | BGP-LS | BGP IP/VPN/EVPN |
           +-----------------+-----+--------+-----------------+
           | T               |     |   X    |                 |
           | T.Insert        |  X  |   X    |                 |
           | T.Insert.Red    |  X  |   X    |                 |
           | T.Encaps        |  X  |   X    |                 |
           | T.Encaps.Red    |  X  |   X    |                 |
           | T.Encaps.L2     |     |   X    |                 |
           | T.Encaps.L2.Red |     |   X    |                 |
           +-----------------+-----+--------+-----------------+

                 Table 2: SRv6 transit behaviors signaling





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   The previous table describes generic capabilities.  It does not
   describe specific instantiated SR policies.

   For example, a BGP-LS advertisement of the T capability of node N
   would indicate that node N supports the basic transit behavior.  The
   T.Insert behavior would describe the capability of node N to perform
   a T.Insert behavior, specifically it would describe how many SIDs
   could be inserted by N without significant performance degradation.
   Same for T.Encaps (the number is potentially lower as the overhead of
   the additional outer IP header is accounted).


   The reader should also remember that any specific instantiated SR
   policy is always assigned a Binding SID.  They should remember that
   BSIDs are advertised in BGP-LS as shown in Table 1.  Hence, it is
   normal that Table 2 only focuses on the generic capabilities related
   to T.Insert and T.Encaps as Table 1 advertises the specific
   instantiated BSID properties.

9.  IANA Considerations

   This document requests the following new IANA registries:

   - A new top-level registry "Segment-routing with IPv6 dataplane
     (SRv6) Parameters" to be created under IANA Protocol registries.
     This registry is being defined to serve as a top-level registry for
     keeping all other SRv6 sub-registries.

   - A sub-registry "SRv6 Endpoint Behaviors" to be defined under top-
     level "Segment-routing with IPv6 dataplane (SRv6) Parameters"
     registry.  This sub-registry maintains 16-bit identifiers for the
     SRv6 Endpoint behaviors.  The range of the registry is 0-65535
     (0x0000 - 0xFFFF) and has the following registration rules and
     allocation policies:

















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   +-------------+---------------+--------------------+----------------+
   | Range       |      Hex      |    Registration    |     Notes      |
   |             |               |     proceadure     |                |
   +-------------+---------------+--------------------+----------------+
   | 0           |     0x0000    |      Reserved      |    Invalid     |
   | 1-32767     | 0x0001-0x7FFF |    IETF review     |     Draft      |
   |             |               |                    | Specifications |
   | 32768-49151 | 0x8000-0xBFFF |    Reserved for    |                |
   |             |               |  experimental use  |                |
   | 49152-65534 | 0xC000-0xFFFE |    Reserved for    |                |
   |             |               |    private use     |                |
   | 65535       |     0xFFFF    |      Reserved      |     Opaque     |
   +-------------+---------------+--------------------+----------------+

                 Table 3: SRv6 Endpoint Behaviors Registry

   The initial registrations for the "Draft Specifications" portion of
   the sub-registry are as follows:

































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        +-------+--------+---------------------------+-----------+
        | Value |  Hex   |     Endpoint function     | Reference |
        +-------+--------+---------------------------+-----------+
        | 1     | 0x0001 |    End (no PSP, no USP)   | [This.ID] |
        | 2     | 0x0002 |        End with PSP       | [This.ID] |
        | 3     | 0x0003 |        End with USP       | [This.ID] |
        | 4     | 0x0004 |      End with PSP&USP     | [This.ID] |
        | 5     | 0x0005 |   End.X (no PSP, no USP)  | [This.ID] |
        | 6     | 0x0006 |       End.X with PSP      | [This.ID] |
        | 7     | 0x0007 |       End.X with USP      | [This.ID] |
        | 8     | 0x0008 |     End.X with PSP&USP    | [This.ID] |
        | 9     | 0x0009 |   End.T (no PSP, no USP)  | [This.ID] |
        | 10    | 0x000A |       End.T with PSP      | [This.ID] |
        | 11    | 0x000B |       End.T with USP      | [This.ID] |
        | 12    | 0x000C |     End.T with PSP&USP    | [This.ID] |
        | 13    | 0x000D |           End.B6          | [This.ID] |
        | 14    | 0x000E |       End.B6.Encaps       | [This.ID] |
        | 15    | 0x000F |           End.BM          | [This.ID] |
        | 16    | 0x0010 |          End.DX6          | [This.ID] |
        | 17    | 0x0011 |          End.DX4          | [This.ID] |
        | 18    | 0x0012 |          End.DT6          | [This.ID] |
        | 19    | 0x0013 |          End.DT4          | [This.ID] |
        | 20    | 0x0014 |          End.DT46         | [This.ID] |
        | 21    | 0x0015 |          End.DX2          | [This.ID] |
        | 22    | 0x0016 |          End.DX2V         | [This.ID] |
        | 23    | 0x0017 |          End.DT2U         | [This.ID] |
        | 24    | 0x0018 |          End.DT2M         | [This.ID] |
        | 25    | 0x0019 |           End.S           | [This.ID] |
        | 26    | 0x001A |         End.B6.Red        | [This.ID] |
        | 27    | 0x001B |     End.B6.Encaps.Red     | [This.ID] |
        | 28    | 0x001C |        End with USD       | [This.ID] |
        | 29    | 0x001D |      End with PSP&USD     | [This.ID] |
        | 30    | 0x001E |      End with USP&USD     | [This.ID] |
        | 31    | 0x001F |  End with PSP, USP & USD  | [This.ID] |
        | 32    | 0x0020 |       End.X with USD      | [This.ID] |
        | 33    | 0x0021 |     End.X with PSP&USD    | [This.ID] |
        | 34    | 0x0022 |     End.X with USP&USD    | [This.ID] |
        | 35    | 0x0023 | End.X with PSP, USP & USD | [This.ID] |
        | 36    | 0x0024 |       End.T with USD      | [This.ID] |
        | 37    | 0x0025 |     End.T with PSP&USD    | [This.ID] |
        | 38    | 0x0026 |     End.T with USP&USD    | [This.ID] |
        | 39    | 0x0027 | End.T with PSP, USP & USD | [This.ID] |
        +-------+--------+---------------------------+-----------+

                  Table 4: IETF - SRv6 Endpoint Behaviors






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10.  Work in progress

   We are working on a extension of this document to provide Yang
   modelling for all the functionality described in this document.  This
   work is ongoing in [I-D.raza-spring-srv6-yang].

11.  Acknowledgements

   The authors would like to acknowledge Stefano Previdi, Dave Barach,
   Mark Townsley, Peter Psenak, Thierry Couture, Kris Michielsen, Paul
   Wells, Robert Hanzl, Dan Ye, Gaurav Dawra, Faisal Iqbal, Jaganbabu
   Rajamanickam, David Toscano, Asif Islam, Jianda Liu, Yunpeng Zhang,
   Jiaoming Li, Narendra A.K, Mike Mc Gourty, Bhupendra Yadav, Sherif
   Toulan, Satish Damodaran, John Bettink, Kishore Nandyala Veera Venk,
   Jisu Bhattacharya and Saleem Hafeez.

12.  Contributors

   Daniel Bernier
   Bell Canada
   Canada

   Email: daniel.bernier@bell.ca

   Dirk Steinberg
   Steinberg Consulting
   Germany

   Email: dws@dirksteinberg.de

   Robert Raszuk
   Bloomberg LP
   United States of America

   Email: robert@raszuk.net

   Bruno Decraene
   Orange
   Frence

   Email: bruno.decraene@orange.com

   Bart Peirens
   Proximus
   Belgium

   Email: bart.peirens@proximus.com




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   Hani Elmalky
   Ericsson
   United States of America

   Email: hani.elmalky@gmail.com

   Prem Jonnalagadda
   Barefoot Networks
   United States of America

   Email: prem@barefootnetworks.com

   Milad Sharif
   Barefoot Networks
   United States of America

   Email: msharif@barefootnetworks.com

   David Lebrun
   Google
   Belgium

   Email: dlebrun@google.com

   Stefano Salsano
   Universita di Roma "Tor Vergata"
   Italy

   Email: stefano.salsano@uniroma2.it

   Ahmed AbdelSalam
   Gran Sasso Science Institute
   Italy

   Email: ahmed.abdelsalam@gssi.it

   Gaurav Naik
   Drexel University
   United States of America

   Email: gn@drexel.edu

   Arthi Ayyangar
   Arista
   United States of America

   Email: arthi@arista.com




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   Satish Mynam
   Innovium Inc.
   United States of America

   Email: smynam@innovium.com

   Wim Henderickx
   Nokia
   Belgium

   Email: wim.henderickx@nokia.com

   Shaowen Ma
   Juniper
   Singapore

   Email: mashao@juniper.net

   Ahmed Bashandy
   Individual
   United States of America

   Email: abashandy.ietf@gmail.com

   Francois Clad
   Cisco Systems, Inc.
   France

   Email: fclad@cisco.com

   Kamran Raza
   Cisco Systems, Inc.
   Canada

   Email: skraza@cisco.com

   Darren Dukes
   Cisco Systems, Inc.
   Canada

   Email: ddukes@cisco.com

   Patrice Brissete
   Cisco Systems, Inc.
   Canada

   Email: pbrisset@cisco.com




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   Zafar Ali
   Cisco Systems, Inc.
   United States of America

   Email: zali@cisco.com

13.  References

13.1.  Normative References

   [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-16 (work in
              progress), February 2019.

   [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>.

   [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>.

13.2.  Informative References

   [I-D.ali-spring-srv6-oam]
              Ali, Z., Filsfils, C., Kumar, N., Pignataro, C.,
              faiqbal@cisco.com, f., Gandhi, R., Leddy, J., Matsushima,
              S., Raszuk, R., daniel.voyer@bell.ca, d., Dawra, G.,
              Peirens, B., Chen, M., and G. Naik, "Operations,
              Administration, and Maintenance (OAM) in Segment Routing
              Networks with IPv6 Data plane (SRv6)", draft-ali-spring-
              srv6-oam-02 (work in progress), October 2018.

   [I-D.bashandy-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extensions to Support Routing over IPv6
              Dataplane", draft-bashandy-isis-srv6-extensions-04 (work
              in progress), October 2018.

   [I-D.dawra-idr-bgpls-srv6-ext]
              Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
              daniel.bernier@bell.ca, d., Uttaro, J., Decraene, B., and
              H. Elmalky, "BGP Link State extensions for IPv6 Segment
              Routing(SRv6)", draft-dawra-idr-bgpls-srv6-ext-04 (work in
              progress), September 2018.



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   [I-D.dawra-idr-srv6-vpn]
              Dawra, G., Filsfils, C., Dukes, D., Brissette, P.,
              Camarillo, P., Leddy, J., daniel.voyer@bell.ca, d.,
              daniel.bernier@bell.ca, d., Steinberg, D., Raszuk, R.,
              Decraene, B., Matsushima, S., and S. Zhuang, "BGP
              Signaling for SRv6 based Services.", draft-dawra-idr-
              srv6-vpn-05 (work in progress), October 2018.

   [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-net-pgm-illustration]
              Filsfils, C., Camarillo, P., Li, Z., Matsushima, S.,
              Decraene, B., Steinberg, D., Lebrun, D., Raszuk, R., and
              J. Leddy, "Illustrations for SRv6 Network Programming",
              draft-filsfils-spring-srv6-net-pgm-illustration-00 (work
              in progress), February 2019.

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

   [I-D.ietf-idr-te-lsp-distribution]
              Previdi, S., Talaulikar, K., Dong, J., Chen, M., Gredler,
              H., and J. Tantsura, "Distribution of Traffic Engineering
              (TE) Policies and State using BGP-LS", draft-ietf-idr-te-
              lsp-distribution-09 (work in progress), June 2018.

   [I-D.ietf-isis-l2bundles]
              Ginsberg, L., Bashandy, A., Filsfils, C., Nanduri, M., and
              E. Aries, "Advertising L2 Bundle Member Link Attributes in
              IS-IS", draft-ietf-isis-l2bundles-07 (work in progress),
              May 2017.

   [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.




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   [I-D.raza-spring-srv6-yang]
              Raza, K., Rajamanickam, J., Liu, X., Hu, Z., Hussain, I.,
              Shah, H., daniel.voyer@bell.ca, d., Elmalky, H.,
              Matsushima, S., Horiba, K., and A. Abdelsalam, "YANG Data
              Model for SRv6 Base and Static", draft-raza-spring-
              srv6-yang-02 (work in progress), October 2018.

   [I-D.xuclad-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca,
              d., Li, C., Decraene, B., Ma, S., Yadlapalli, C.,
              Henderickx, W., and S. Salsano, "Service Programming with
              Segment Routing", draft-xuclad-spring-sr-service-
              programming-01 (work in progress), October 2018.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
              December 1998, <https://www.rfc-editor.org/info/rfc2473>.

   [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>.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <https://www.rfc-editor.org/info/rfc6437>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

Authors' Addresses

   Clarence Filsfils
   Cisco Systems, Inc.
   Belgium

   Email: cf@cisco.com


   Pablo Camarillo Garvia (editor)
   Cisco Systems, Inc.
   Spain

   Email: pcamaril@cisco.com





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Internet-Draft          SRv6 Network Programming           February 2019


   John Leddy
   Comcast
   United States of America

   Email: john_leddy@cable.comcast.com


   Daniel Voyer
   Bell Canada
   Canada

   Email: daniel.voyer@bell.ca


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

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


   Zhenbin Li
   Huawei Technologies
   China

   Email: lizhenbin@huawei.com























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