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Segment Routing over IPv6 (SRv6) Network Programming
RFC 8986

Document Type RFC - Proposed Standard (February 2021) Errata IPR
Authors Clarence Filsfils , Pablo Camarillo , John Leddy , Daniel Voyer , Satoru Matsushima , Zhenbin Li
Last updated 2022-05-27
RFC stream Internet Engineering Task Force (IETF)
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Additional resources Mailing list discussion
IESG Responsible AD Martin Vigoureux
Send notices to (None)
RFC 8986
gt; Last Entry+1)) {
   S10.      Send an ICMP Parameter Problem to the Source Address
                with Code 0 (Erroneous header field encountered)
                and Pointer set to the Segments Left field,
                interrupt packet processing, and discard the packet.

   S11.   }
   S12.   Decrement IPv6 Hop Limit by 1
   S13.   Decrement Segments Left by 1
   S14.   Update IPv6 DA with Segment List[Segments Left]
   S15.   Push the MPLS label stack for B
   S16.   Submit the packet to the MPLS engine for transmission
   S17. }

   When processing the Upper-Layer header of a packet matching a FIB
   entry locally instantiated as an End.BM SID, process the packet as
   per Section 4.1.1.

4.16.  Flavors

   The Penultimate Segment Pop (PSP) of the SRH, Ultimate Segment Pop
   (USP) of the SRH, and Ultimate Segment Decapsulation (USD) flavors
   are variants of the End, End.X, and End.T behaviors.  The End, End.X,
   and End.T behaviors can support these flavors either individually or
   in combinations.

4.16.1.  PSP: Penultimate Segment Pop of the SRH

4.16.1.1.  Guidelines

   SR Segment Endpoint Nodes advertise the SIDs instantiated on them via
   control-plane protocols as described in Section 8.  Different
   behavior IDs are allocated for flavored and unflavored SIDs (see
   Table 6).

   An SR Segment Endpoint Node that offers both PSP- and non-PSP-
   flavored behavior advertises them as two different SIDs.

   The SR Segment Endpoint Node only advertises the PSP flavor if the
   operator enables this capability at the node.

   The PSP operation is deterministically controlled by the SR source
   node.

   A PSP-flavored SID is used by the SR source node when it needs to
   instruct the penultimate SR Segment Endpoint Node listed in the SRH
   to remove the SRH from the IPv6 header.

4.16.1.2.  Definition

   SR Segment Endpoint Nodes receive the IPv6 packet with the
   Destination Address field of the IPv6 header equal to its SID
   address.

   A penultimate SR Segment Endpoint Node is one that, as part of the
   SID processing, copies the last SID from the SRH into the IPv6
   Destination Address and decrements the Segments Left value from one
   to zero.

   The PSP operation only takes place at a penultimate SR Segment
   Endpoint Node and does not happen at any transit node.  When a SID of
   PSP flavor is processed at a non-penultimate SR Segment Endpoint
   Node, the PSP behavior is not performed as described in the
   pseudocode below since Segments Left would not be zero.

   The SRH processing of the End, End.X, and End.T behaviors are
   modified: after the instruction "S14.  Update IPv6 DA with Segment
   List[Segments Left]" is executed, the following instructions must be
   executed as well:

   S14.1.   If (Segments Left == 0) {
   S14.2.      Update the Next Header field in the preceding header to
                  the Next Header value from the SRH
   S14.3.      Decrease the IPv6 header Payload Length by
                  8*(Hdr Ext Len+1)
   S14.4.      Remove the SRH from the IPv6 extension header chain
   S14.5.   }

   The usage of PSP does not increase the MTU of the IPv6 packet and
   hence does not have any impact on the Path MTU (PMTU) discovery
   mechanism.

   As a reminder, Section 5 of [RFC8754] defines the SR Deployment Model
   within the SR Domain [RFC8402].  Within this framework, the
   Authentication Header (AH) is not used to secure the SRH as described
   in Section 7.5 of [RFC8754].  Hence, the discussion of applicability
   of PSP along with AH usage is beyond the scope of this document.

   In the context of this specification, the End, End.X, and End.T
   behaviors with PSP do not contravene Section 4 of [RFC8200] because
   the destination address of the incoming packet is the address of the
   node executing the behavior.

4.16.1.3.  Use Case

   One use case for the PSP functionality is streamlining the operation
   of an egress border router.

     +----------------------------------------------------+
     |                                                    |
   +-+-+         +--+         +--+         +--+         +-+-+
   |iPE+-------->+R2+-------->+R3+-------->+R4+-------->+ePE|
   | R1|         +--+         +--+         +--+         |R5 |
   +-+-+ +-----+      +-----+      +-----+      +-----+ +-+-+
     |   |IPv6 |      |IPv6 |      |IPv6 |      |IPv6 |   |
     |   |DA=R3|      |DA=R3|      |DA=R5|      |DA=R5|   |
     |   +-----+      +-----+      +-----+      +-----+   |
     |   | SRH |      | SRH |      | IP  |      | IP  |   |
     |   |SL=1 |      |SL=1 |      +-----+      +-----+   |
     |   | R5  |      | R5  |                             |
     |   +-----+      +-----+                             |
     |   | IP  |      | IP  |                             |
     |   +-----+      +-----+                             |
     |                                                    |
     +----------------------------------------------------+

                      Figure 1: PSP Use Case Topology

   In the above illustration, for a packet sent from the ingress
   provider edge (iPE) to the egress provider edge (ePE), node R3 is an
   intermediate traffic-engineering waypoint and is the penultimate
   segment endpoint router; this node copies the last segment from the
   SRH into the IPv6 Destination Address and decrements Segments Left to
   0.  The Software-Defined Networking (SDN) controller knows that no
   other node after R3 needs to inspect the SRH, and it instructs R3 to
   remove the exhausted SRH from the packet by using a PSP-flavored SID.

   The benefits for the egress PE are straightforward:

   *  As part of the decapsulation process, the egress PE is required to
      parse and remove fewer bytes from the packet.

   *  If a lookup on an upper-layer IP header is required (e.g., per-VRF
      VPN), the header is more likely to be within the memory accessible
      to the lookup engine in the forwarding ASIC (Application-Specific
      Integrated Circuit).

4.16.2.  USP: Ultimate Segment Pop of the SRH

   The SRH processing of the End, End.X, and End.T behaviors are
   modified; the instructions S02-S04 are substituted by the following
   ones:

   S02.     If (Segments Left == 0) {
   S03.1.      Update the Next Header field in the preceding header to
                  the Next Header value of the SRH
   S03.2.      Decrease the IPv6 header Payload Length by
                  8*(Hdr Ext Len+1)
   S03.3.      Remove the SRH from the IPv6 extension header chain
   S03.4.      Proceed to process the next header in the packet
   S04.     }

   One of the applications of the USP flavor is when a packet with an
   SRH is destined to an application on hosts with smartNICs ("Smart
   Network Interface Cards") implementing SRv6.  The USP flavor is used
   to remove the consumed SRH from the extension header chain before
   sending the packet to the host.

4.16.3.  USD: Ultimate Segment Decapsulation

   The Upper-Layer header processing of the End, End.X, and End.T
   behaviors are modified as follows:

   End:

   S01. If (Upper-Layer header type == 41(IPv6) ) {
   S02.    Remove the outer IPv6 header with all its extension headers
   S03.    Submit the packet to the egress IPv6 FIB lookup for
              transmission to the new destination
   S04. } Else if (Upper-Layer header type == 4(IPv4) ) {
   S05.    Remove the outer IPv6 header with all its extension headers
   S06.    Submit the packet to the egress IPv4 FIB lookup for
              transmission to the new destination
   S07. Else {
   S08.    Process as per Section 4.1.1
   S09. }

   End.T:

   S01. If (Upper-Layer header type == 41(IPv6) ) {
   S02.    Remove the outer IPv6 header with all its extension headers
   S03.    Set the packet's associated FIB table to T
   S04.    Submit the packet to the egress IPv6 FIB lookup for
              transmission to the new destination
   S05. } Else if (Upper-Layer header type == 4(IPv4) ) {
   S06.    Remove the outer IPv6 header with all its extension headers
   S07.    Set the packet's associated FIB table to T
   S08.    Submit the packet to the egress IPv4 FIB lookup for
              transmission to the new destination
   S09. Else {
   S10.    Process as per Section 4.1.1
   S11. }

   End.X:

   S01. If (Upper-Layer header type == 41(IPv6) ||
             Upper-Layer header type == 4(IPv4) ) {
   S02.    Remove the outer IPv6 header with all its extension headers
   S03.    Forward the exposed IP packet to the L3 adjacency J
   S04. } Else {
   S05.    Process as per Section 4.1.1
   S06. }

   One of the applications of the USD flavor is the case of a Topology
   Independent Loop-Free Alternate (TI-LFA) in P routers with
   encapsulation.  The USD flavor allows the last SR Segment Endpoint
   Node in the repair path list to decapsulate the IPv6 header added at
   the TI-LFA Point of Local Repair and forward the inner packet.

5.  SR Policy Headend Behaviors

   This section describes a set of SRv6 Policy Headend [RFC8402]
   behaviors.

    +-----------------+-----------------------------------------------+
    | H.Encaps        | SR Headend with Encapsulation in an SR Policy |
    +-----------------+-----------------------------------------------+
    | H.Encaps.Red    | H.Encaps with Reduced Encapsulation           |
    +-----------------+-----------------------------------------------+
    | H.Encaps.L2     | H.Encaps Applied to Received L2 Frames        |
    +-----------------+-----------------------------------------------+
    | H.Encaps.L2.Red | H.Encaps.Red Applied to Received L2 Frames    |
    +-----------------+-----------------------------------------------+

                    Table 2: SR Policy Headend Behaviors

   This list is not exhaustive, and future documents may define
   additional behaviors.

5.1.  H.Encaps: SR Headend with Encapsulation in an SR 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.

   Node N is configured with an IPv6 address T (e.g., assigned to its
   loopback).

   N steers the transit packets P1 and P2 into an SRv6 Policy with a
   Source Address T and a segment list <S1, S2, S3>.

   The H.Encaps encapsulation behavior is defined as follows:

   S01.   Push an IPv6 header with its own SRH
   S02.   Set outer IPv6 SA = T and outer IPv6 DA to the first SID
             in the segment list
   S03.   Set outer Payload Length, Traffic Class, Hop Limit, and
             Flow Label fields
   S04.   Set the outer Next Header value
   S05.   Decrement inner IPv6 Hop Limit or IPv4 TTL
   S06.   Submit the packet to the IPv6 module for transmission to S1

      |  Note:
      |  
      |  S03: As described in [RFC2473] and [RFC6437].

   After the H.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 received packet is encapsulated unmodified (with the exception of
   the IPv4 TTL or IPv6 Hop Limit that is decremented as described in
   [RFC2473]).

   The H.Encaps behavior is valid for any kind of L3 traffic.  This
   behavior is commonly used for L3VPN with IPv4 and IPv6 deployments.
   It may be also used for TI-LFA [SR-TI-LFA] at the Point of Local
   Repair.

   The push of 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.

5.2.  H.Encaps.Red: H.Encaps with Reduced Encapsulation

   The H.Encaps.Red behavior is an optimization of the H.Encaps
   behavior.

   H.Encaps.Red reduces the length of the SRH by excluding the first SID
   in the SRH of the pushed IPv6 header.  The first SID is only placed
   in the Destination Address field of the pushed IPv6 header.

   After the H.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 push of 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.

5.3.  H.Encaps.L2: H.Encaps Applied to Received L2 Frames

   The H.Encaps.L2 behavior encapsulates a received Ethernet
   [IEEE.802.3_2018] frame and its attached VLAN header, if present, in
   an IPv6 packet with an SRH.  The Ethernet frame becomes the payload
   of the new IPv6 packet.

   The Next Header field of the SRH MUST be set to 143.

   The push of 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.

   The encapsulating node MUST remove the preamble (if any) and frame
   check sequence (FCS) from the Ethernet frame upon encapsulation, and
   the decapsulating node MUST regenerate, as required, the preamble and
   FCS before forwarding the Ethernet frame.

5.4.  H.Encaps.L2.Red: H.Encaps.Red Applied to Received L2 Frames

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

   H.Encaps.L2.Red reduces the length of the SRH by excluding the first
   SID in the SRH of the pushed IPv6 header.  The first SID is only
   placed in the Destination Address field of the pushed IPv6 header.

   The push of 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.

6.  Counters

   A node supporting this document SHOULD implement a pair of traffic
   counters (one for packets and one for bytes) per local SID entry, for
   traffic that matched that SID and was processed successfully (i.e.,
   packets that generate ICMP Error Messages or are dropped are not
   counted).  The retrieval of these counters from MIB, NETCONF/YANG, or
   any other data structure is outside the scope of this document.

7.  Flow-Based Hash Computation

   When a flow-based selection within a set needs to be performed, the
   IPv6 Source Address, the IPv6 Destination Address, and the IPv6 Flow
   Label of the outer IPv6 header MUST be included in the flow-based
   hash.

   This may occur in any of the following scenarios:

   *  A FIB lookup is performed and multiple ECMP paths exist to the
      updated destination address.

   *  End.X, End.DX4, or End.DX6 is bound to an array of adjacencies.

   *  The packet is steered in an SR Policy whose selected path has
      multiple SID lists.

   Additionally, any transit router in an SRv6 domain includes the outer
   flow label in its ECMP flow-based hash [RFC6437].

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 of
   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, and others to complex
   applications residing in VMs and containers.

   While not necessary for an SDN control plane, the remainder of this
   section provides a high-level illustrative overview of how control-
   plane protocols may be involved with SRv6.  Their specification is
   outside the scope of this document.

8.1.  IGP

   The End, End.T, and End.X SIDs express topological behaviors and
   hence are expected to be signaled in the IGP together with the
   flavors PSP, USP, and USD.  The IGP should also advertise the Maximum
   SID Depth (MSD) capability of the node for each type of SRv6
   operation -- in particular, the SR source (e.g., H.Encaps),
   intermediate endpoint (e.g., End and End.X), and final endpoint
   (e.g., End.DX4 and End.DT6) behaviors.  These capabilities are
   factored in by an SR source node (or a controller) during the SR
   Policy computation.

   The presence of SIDs in the IGP does not imply any routing semantics
   to the addresses represented by these SIDs.  The routing reachability
   to an IPv6 address is solely governed by the non-SID-related IGP
   prefix reachability information that includes locators.  Routing is
   neither governed nor influenced in any way by a SID advertisement in
   the IGP.

   These SIDs provide important topological behaviors for the IGP to
   build Fast Reroute (FRR) solutions based on TI-LFA [SR-TI-LFA] and
   for TE processes relying on an IGP topology database to build SR
   Policies.

8.2.  BGP-LS

   BGP-LS provides the functionality for topology discovery that
   includes the SRv6 capabilities of the nodes, their locators, and
   locally instantiated SIDs.  This enables controllers or applications
   to build an inter-domain topology that can be used for computation of
   SR Policies using the SRv6 SIDs.

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 can be signaled in BGP.

   In some scenarios, an egress PE advertising a VPN route might wish to
   abstract the specific behavior bound to the SID from the ingress PE
   and other routers in the network.  In such case, the SID may be
   advertised using the Opaque SRv6 Endpoint Behavior codepoint defined
   in Table 6.  The details of such control-plane signaling mechanisms
   are out of the scope of this document.

8.4.  Summary

   The following table summarizes which SID behaviors may be signaled in
   which control-plane 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.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.DX2               |     |   X    |        X        |
        +-----------------------+-----+--------+-----------------+
        | End.DX2V              |     |   X    |        X        |
        +-----------------------+-----+--------+-----------------+
        | End.DT2U              |     |   X    |        X        |
        +-----------------------+-----+--------+-----------------+
        | End.DT2M              |     |   X    |        X        |
        +-----------------------+-----+--------+-----------------+
        | End.B6.Encaps         |     |   X    |                 |
        +-----------------------+-----+--------+-----------------+
        | End.B6.Encaps.Red     |     |   X    |                 |
        +-----------------------+-----+--------+-----------------+
        | End.B6.BM             |     |   X    |                 |
        +-----------------------+-----+--------+-----------------+

            Table 3: SRv6 Locally Instantiated SIDs Signaling

   The following table summarizes which SR Policy Headend capabilities
   may be signaled in which control-plane protocol.

           +=================+=====+========+=================+
           |                 | IGP | BGP-LS | BGP IP/VPN/EVPN |
           +=================+=====+========+=================+
           | H.Encaps        |  X  |   X    |                 |
           +-----------------+-----+--------+-----------------+
           | H.Encaps.Red    |  X  |   X    |                 |
           +-----------------+-----+--------+-----------------+
           | H.Encaps.L2     |     |   X    |                 |
           +-----------------+-----+--------+-----------------+
           | H.Encaps.L2.Red |     |   X    |                 |
           +-----------------+-----+--------+-----------------+

             Table 4: SRv6 Policy Headend Behaviors Signaling

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

   For example, a BGP-LS advertisement of H.Encaps behavior would
   describe the capability of node N to perform H.Encaps behavior.
   Specifically, it would describe how many SIDs could be pushed by N
   without significant performance degradation.

   As a reminder, an SR Policy is always assigned a Binding SID
   [RFC8402].  Binding SIDs are also advertised in BGP-LS as shown in
   Table 3.  Hence, Table 4 only focuses on the generic capabilities
   related to H.Encaps.

9.  Security Considerations

   The security considerations for Segment Routing are discussed in
   [RFC8402].  Section 5 of [RFC8754] describes the SR Deployment Model
   and the requirements for securing the SR Domain.  The security
   considerations of [RFC8754] also cover topics such as attack vectors
   and their mitigation mechanisms that also apply the behaviors
   introduced in this document.  Together, they describe the required
   security mechanisms that allow establishment of an SR domain of
   trust.  Having such a well-defined trust boundary is necessary in
   order to operate SRv6-based services for internal traffic while
   preventing any external traffic from accessing or exploiting the
   SRv6-based services.  Care and rigor in IPv6 address allocation for
   use for SRv6 SID allocations and network infrastructure addresses, as
   distinct from IPv6 addresses allocated for end users and systems (as
   illustrated in Section 5.1 of [RFC8754]), can provide the clear
   distinction between internal and external address space that is
   required to maintain the integrity and security of the SRv6 Domain.
   Additionally, [RFC8754] defines a Hashed Message Authentication Code
   (HMAC) TLV permitting SR Segment Endpoint Nodes in the SR domain to
   verify that the SRH applied to a packet was selected by an authorized
   party and to ensure that the segment list is not modified after
   generation, regardless of the number of segments in the segment list.
   When enabled by local configuration, HMAC processing occurs at the
   beginning of SRH processing as defined in Section 2.1.2.1 of
   [RFC8754].

   This document introduces SRv6 Endpoint and SR Policy Headend
   behaviors for implementation on SRv6-capable nodes in the network.
   The definition of the SR Policy Headend should be consistent with the
   specific behavior used and any local configuration (as specified in
   Section 4.1.1).  As such, this document does not introduce any new
   security considerations.

   The SID behaviors specified in this document have the same HMAC TLV
   handling and mutability properties with regard to the Flags, Tag, and
   Segment List field as the SID behavior specified in [RFC8754].

10.  IANA Considerations

10.1.  Ethernet Next Header Type

   IANA has allocated "Ethernet" (value 143) in the "Assigned Internet
   Protocol Numbers" registry (see <https://www.iana.org/assignments/
   protocol-numbers/>).  Value 143 in the Next Header field of an IPv6
   header or any extension header indicates that the payload is an
   Ethernet frame [IEEE.802.3_2018].

10.2.  SRv6 Endpoint Behaviors Registry

   IANA has created a new top-level registry called "Segment Routing"
   (see <https://www.iana.org/assignments/segment-routing/>).  This
   registry serves as a top-level registry for all Segment Routing
   subregistries.

   Additionally, IANA has created a new subregistry called "SRv6
   Endpoint Behaviors" under the top-level "Segment Routing" registry.
   This subregistry maintains 16-bit identifiers for the SRv6 Endpoint
   behaviors.  This registry is established to provide consistency for
   control-plane protocols that need to refer to these behaviors.  These
   values are not encoded in the function bits within a SID.

10.2.1.  Registration Procedures

   The range of the registry is 0-65535 (0x0000-0xFFFF).  The table
   below contains the allocation ranges and registration policies
   [RFC8126] for each:

   +=============+===============+=========================+===========+
   | Range       |  Range (Hex)  |       Registration      |    Note   |
   |             |               |        Procedures       |           |
   +=============+===============+=========================+===========+
   | 0           |     0x0000    |         Reserved        | Not to be |
   |             |               |                         | allocated |
   +-------------+---------------+-------------------------+-----------+
   | 1-32767     | 0x0001-0x7FFF |        First Come       |           |
   |             |               |       First Served      |           |
   +-------------+---------------+-------------------------+-----------+
   | 32768-34815 | 0x8000-0x87FF |       Private Use       |           |
   +-------------+---------------+-------------------------+-----------+
   | 34816-65534 | 0x8800-0xFFFE |         Reserved        |           |
   +-------------+---------------+-------------------------+-----------+
   | 65535       |     0xFFFF    |         Reserved        |   Opaque  |
   +-------------+---------------+-------------------------+-----------+

                      Table 5: Registration Procedures

10.2.2.  Initial Registrations

   The initial registrations for the subregistry are as follows:

   +=============+===============+=========================+===========+
   | Value       |      Hex      |    Endpoint Behavior    | Reference |
   +=============+===============+=========================+===========+
   | 0           |     0x0000    |         Reserved        |           |
   +-------------+---------------+-------------------------+-----------+
   | 1           |     0x0001    |           End           |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 2           |     0x0002    |       End with PSP      |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 3           |     0x0003    |       End with USP      |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 4           |     0x0004    |    End with PSP & USP   |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 5           |     0x0005    |          End.X          |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 6           |     0x0006    |      End.X with PSP     |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 7           |     0x0007    |      End.X with USP     |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 8           |     0x0008    |   End.X with PSP & USP  |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 9           |     0x0009    |          End.T          |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 10          |     0x000A    |      End.T with PSP     |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 11          |     0x000B    |      End.T with USP     |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 12          |     0x000C    |   End.T with PSP & USP  |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 13          |     0x000D    |        Unassigned       |           |
   +-------------+---------------+-------------------------+-----------+
   | 14          |     0x000E    |      End.B6.Encaps      |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 15          |     0x000F    |          End.BM         |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 16          |     0x0010    |         End.DX6         |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 17          |     0x0011    |         End.DX4         |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 18          |     0x0012    |         End.DT6         |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 19          |     0x0013    |         End.DT4         |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 20          |     0x0014    |         End.DT46        |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 21          |     0x0015    |         End.DX2         |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 22          |     0x0016    |         End.DX2V        |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 23          |     0x0017    |         End.DT2U        |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 24          |     0x0018    |         End.DT2M        |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 25          |     0x0019    |         Reserved        |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 26          |     0x001A    |        Unassigned       |           |
   +-------------+---------------+-------------------------+-----------+
   | 27          |     0x001B    |    End.B6.Encaps.Red    |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 28          |     0x001C    |       End with USD      |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 29          |     0x001D    |    End with PSP & USD   |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 30          |     0x001E    |    End with USP & USD   |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 31          |     0x001F    |   End with PSP, USP &   |  RFC 8986 |
   |             |               |           USD           |           |
   +-------------+---------------+-------------------------+-----------+
   | 32          |     0x0020    |      End.X with USD     |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 33          |     0x0021    |   End.X with PSP & USD  |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 34          |     0x0022    |   End.X with USP & USD  |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 35          |     0x0023    |   End.X with PSP, USP   |  RFC 8986 |
   |             |               |          & USD          |           |
   +-------------+---------------+-------------------------+-----------+
   | 36          |     0x0024    |      End.T with USD     |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 37          |     0x0025    |   End.T with PSP & USD  |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 38          |     0x0026    |   End.T with USP & USD  |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 39          |     0x0027    |   End.T with PSP, USP   |  RFC 8986 |
   |             |               |          & USD          |           |
   +-------------+---------------+-------------------------+-----------+
   | 40-32766    | 0x0028-0x7FFE |        Unassigned       |           |
   +-------------+---------------+-------------------------+-----------+
   | 32767       |     0x7FFF    |    The SID defined in   | RFC 8986, |
   |             |               |         RFC 8754        |  RFC 8754 |
   +-------------+---------------+-------------------------+-----------+
   | 32768-34815 | 0x8000-0x87FF |   Reserved for Private  |  RFC 8986 |
   |             |               |           Use           |           |
   +-------------+---------------+-------------------------+-----------+
   | 34816-65534 | 0x8800-0xFFFE |         Reserved        |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+
   | 65535       |     0xFFFF    |          Opaque         |  RFC 8986 |
   +-------------+---------------+-------------------------+-----------+

                       Table 6: Initial Registrations

11.  References

11.1.  Normative References

   [IEEE.802.3_2018]
              IEEE, "IEEE Standard for Ethernet", IEEE 802.3-2018,
              DOI 10.1109/IEEESTD.2018.8457469, 31 August 2018,
              <https://ieeexplore.ieee.org/document/8457469>.

   [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>.

   [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>.

   [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>.

   [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>.

   [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>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/info/rfc8754>.

11.2.  Informative References

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
              <https://www.rfc-editor.org/info/rfc4193>.

   [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>.

   [RFC4664]  Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
              2 Virtual Private Networks (L2VPNs)", RFC 4664,
              DOI 10.17487/RFC4664, September 2006,
              <https://www.rfc-editor.org/info/rfc4664>.

   [RFC4761]  Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
              <https://www.rfc-editor.org/info/rfc4761>.

   [RFC4762]  Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private
              LAN Service (VPLS) Using Label Distribution Protocol (LDP)
              Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007,
              <https://www.rfc-editor.org/info/rfc4762>.

   [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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8214]  Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
              Rabadan, "Virtual Private Wire Service Support in Ethernet
              VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
              <https://www.rfc-editor.org/info/rfc8214>.

   [RFC8317]  Sajassi, A., Ed., Salam, S., Drake, J., Uttaro, J.,
              Boutros, S., and J. Rabadan, "Ethernet-Tree (E-Tree)
              Support in Ethernet VPN (EVPN) and Provider Backbone
              Bridging EVPN (PBB-EVPN)", RFC 8317, DOI 10.17487/RFC8317,
              January 2018, <https://www.rfc-editor.org/info/rfc8317>.

   [SR-TI-LFA]
              Litkowski, S., Bashandy, A., Filsfils, C., Francois, P.,
              Decraene, B., and D. Voyer, "Topology Independent Fast
              Reroute using Segment Routing", Work in Progress,
              Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
              06, 1 February 2021, <https://tools.ietf.org/html/draft-
              ietf-rtgwg-segment-routing-ti-lfa-06>.

   [SRV6-NET-PGM-ILLUST]
              Filsfils, C., Camarillo, P., Ed., Li, Z., Matsushima, S.,
              Decraene, B., Steinberg, D., Lebrun, D., Raszuk, R., and
              J. Leddy, "Illustrations for SRv6 Network Programming",
              Work in Progress, Internet-Draft, draft-filsfils-spring-
              srv6-net-pgm-illustration-03, 25 September 2020,
              <https://tools.ietf.org/html/draft-filsfils-spring-srv6-
              net-pgm-illustration-03>.

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, Saleem Hafeez, and Brian Carpenter.

Contributors

   Daniel Bernier
   Bell Canada
   Canada

   Email: daniel.bernier@bell.ca

   Dirk Steinberg
   Lapishills Consulting Limited
   Cyprus

   Email: dirk@lapishills.com

   Robert Raszuk
   Bloomberg LP
   United States of America

   Email: robert@raszuk.net

   Bruno Decraene
   Orange
   France

   Email: bruno.decraene@orange.com

   Bart Peirens
   Proximus
   Belgium

   Email: bart.peirens@proximus.com

   Hani Elmalky
   Google
   United States of America

   Email: helmalky@google.com

   Prem Jonnalagadda
   Barefoot Networks
   United States of America

   Email: prem@barefootnetworks.com

   Milad Sharif
   SambaNova Systems
   United States of America

   Email: milad.sharif@sambanova.ai

   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
   Arrcus, Inc
   United States of America

   Email: arthi@arrcus.com

   Satish Mynam
   Arrcus, Inc
   United States of America

   Email: satishm@arrcus.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

   Zafar Ali
   Cisco Systems, Inc.
   United States of America

   Email: zali@cisco.com

   Ketan Talaulikar
   Cisco Systems, Inc.
   India

   Email: ketant@cisco.com

Authors' Addresses

   Clarence Filsfils (editor)
   Cisco Systems, Inc.
   Belgium

   Email: cf@cisco.com

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

   Email: pcamaril@cisco.com

   John Leddy
   Akamai Technologies
   United States of America

   Email: john@leddy.net

   Daniel Voyer
   Bell Canada
   Canada

   Email: daniel.voyer@bell.ca

   Satoru Matsushima
   SoftBank
   Japan

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

   Zhenbin Li
   Huawei Technologies
   China

   Email: lizhenbin@huawei.com