The IPv6 Compact Routing Header (CRH)
draft-bonica-6man-comp-rtg-hdr-27

Document Type Active Internet-Draft (individual)
Authors Ron Bonica  , Yuji Kamite  , Andrew Alston  , Daniam Henriques  , Luay Jalil 
Last updated 2021-11-15
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6man                                                           R. Bonica
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                               Y. Kamite
Expires: 16 May 2022                      NTT Communications Corporation
                                                               A. Alston
                                                            D. Henriques
                                                          Liquid Telecom
                                                                L. Jalil
                                                                 Verizon
                                                        12 November 2021

                 The IPv6 Compact Routing Header (CRH)
                   draft-bonica-6man-comp-rtg-hdr-27

Abstract

   This document defines two new Routing header types.  Collectively,
   they are called the Compact Routing Headers (CRH).  Individually,
   they are called CRH-16 and CRH-32.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on 16 May 2022.

Copyright Notice

   Copyright (c) 2021 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
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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components

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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  The Compressed Routing Headers (CRH)  . . . . . . . . . . . .   3
   4.  The CRH Forwarding Information Base (CRH-FIB) . . . . . . . .   4
   5.  Processing Rules  . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Computing Minimum CRH Length  . . . . . . . . . . . . . .   7
     5.2.  CRH Removal Procedure . . . . . . . . . . . . . . . . . .   8
   6.  Mutability  . . . . . . . . . . . . . . . . . . . . . . . . .   8
   7.  Applications And SIDs . . . . . . . . . . . . . . . . . . . .   8
   8.  Management Considerations . . . . . . . . . . . . . . . . . .   9
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   10. Implementation and Deployment Status  . . . . . . . . . . . .   9
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     14.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  CRH Processing Examples  . . . . . . . . . . . . . .  12
     A.1.  The SID List Contains One Entry For Each Segment In The
           Path  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     A.2.  The SID List Omits The First Entry In The Path  . . . . .  14
   Appendix B.  A Packet Recycling Use-Case  . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   IPv6 [RFC8200] source nodes use Routing headers to specify the path
   that a packet takes to its destination.  The IETF has defined several
   Routing header types [IANA-RH].  This document defines two new
   Routing header types.  Collectively, they are called the Compact
   Routing Headers (CRH).  Individually, they are called CRH-16 and CRH-
   32.

   The CRH allows IPv6 source nodes to specify the path that a packet
   takes to its destination.  The CRH:

   *  Can be encoded in relatively few bytes.

   *  Is designed to operate within a network domain.  (See Section 9).

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   The following are reasons for encoding the CRH in as few bytes as
   possible:

   *  Many ASIC-based forwarders copy headers from buffer memory to on-
      chip memory.  As header sizes increase, so does the cost of this
      copy.

   *  Because Path MTU Discovery (PMTUD) [RFC8201] is not entirely
      reliable, many IPv6 hosts refrain from sending packets larger than
      the IPv6 minimum link MTU (i.e., 1280 bytes).  When packets are
      small, the overhead imposed by large Routing Headers is excessive.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  The Compressed Routing Headers (CRH)

   Both CRH versions (i.e., CRH-16 and CRH-32) contain the following
   fields:

   *  Next Header - Defined in [RFC8200].

   *  Hdr Ext Len - Defined in [RFC8200].

   *  Routing Type - Defined in [RFC8200].  Value TBD by IANA.  (For
      CRH-16, the suggested value is 5.  For CRH-32, the suggested value
      is 6.)

   *  Segments Left - Defined in [RFC8200].

   *  Type-specific Data - Described in [RFC8200].

   In the CRH, the Type-specific data field contains a list of Segment
   Identifiers (SIDs).  Each SID represents both of the following:

   *  A segment of the path that the packet takes to its destination.

   *  An entry in the CRH Forwarding Information Base (CRH-FIB)
      (Section 4).

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   SIDs are listed in reverse order.  So, the first SID in the list
   represents the final segment in the path.  Because segments are
   listed in reverse order, the Segments Left field can be used as an
   index into the SID list.  In this document, the "current SID" is the
   SID list entry referenced by the Segments Left field.

   The first segment in the path can be omitted from the list.  See
   Appendix A for examples.

   In the CRH-16 (Figure 1), each SID is encoded in 16-bits.  In the
   CRH-32 (Figure 2), each SID is encoded in 32-bits.

   In all cases, the CRH MUST end on a 64-bit boundary.  So, the Type-
   specific data field MUST be padded with zeros if the CRH would
   otherwise not end on a 64-bit boundary.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Next Header  |  Hdr Ext Len  | Routing Type  | Segments Left |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |             SID[0]            |          SID[1]               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
     |                          .........
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

                              Figure 1: CRH-16

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Next Header  |  Hdr Ext Len  | Routing Type  | Segments Left |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     +                             SID[0]                            +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     +                             SID[1]                            +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     //                                                              //
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     +                             SID[n]                            +
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                              Figure 2: CRH-32

4.  The CRH Forwarding Information Base (CRH-FIB)

   Each SID identifies a CRH-FIB entry.

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   Each CRH-FIB entry contains:

   *  An IPv6 address (optional).

   *  A topological function.

   *  Arguments for the topological function (optional).

   *  Flags.

   *  A service function (optional).

   *  Arguments for the service function (optional).

   The IPv6 address can represent either:

   *  An interface on the next segment endpoint.

   *  An SRv6 SID [RFC8986], instantiated on the next segment endpoint.

   The first ten bits of the IPv6 address MUST NOT be fe00.  That prefix
   is reserved for link-local [RFC6890] addresses.

   The topological function specifies how the processing node forwards
   the packet to the next segment endpoint.  The following are examples:

   *  Forward the packet through the least-cost path to the next segment
      endpoint.

   *  Forward the packet through a specified interface.

   *  Encapsulate the packet in another IPv6 header of any type (e.g.,
      MPLS, IPv6) and forward either through the least cost path or a
      specified interface.

   *  Recycle the packet, as if the node had forwarded to one of its own
      interfaces.  When recycling is complete, process the next SID.
      See Appendix B for a packet recycling use-case.

   Some topological functions require parameters.  For example, a
   topological function might require a parameter that identifies the
   interface through which the packet should be forwarded.

   The following flags are defined:

   *  The PSP flag indicates whether the penultimate segment endpoint
      (i.e., the node that sets Segments Left to 0) MAY remove the CRH.

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   *  The OAM flag indicates whether the processing node should invoke
      OAM procedures for which it is configured.

   The service function is optional.  If present, it invokes a node
   specific procedure.  The following are examples of node specific
   procedures:

   *  Emit telemetry.

   *  Subject the packet's payload to a firewall rule.

   *  Replicate the packet, forwarding one copy and retaining the other
      for sampling, analysis, or other purposes.

   Node specific procedures are not subject to standardization.  A node
   can support any number of node specific procedures and associate them
   with any SIDs.

   Some service functions require parameters.  For example, an
   instruction to emit telemetry might require an IP address to which
   telemetry should be sent.

   The CRH-FIB can be populated:

   *  By an operator, using a Command Line Interface (CLI).

   *  By a controller, using the Path Computation Element (PCE)
      Communication Protocol (PCEP) [RFC5440] or the Network
      Configuration Protocol (NETCONF) [RFC6241].

   *  By a distributed routing protocol [ISO10589-Second-Edition],
      [RFC5340], [RFC4271].

5.  Processing Rules

   The following rules describe CRH processing:

   *  If Segments Left equals 0, skip over the CRH and process the next
      header in the packet.

   *  If Hdr Ext Len indicates that the CRH is larger than the
      implementation can process, discard the packet and send an ICMPv6
      [RFC4443] Parameter Problem, Code 0, message to the Source
      Address, pointing to the Hdr Ext Len field.

   *  Compute L, the minimum CRH length ( Section 5.1).

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   *  If L is greater than Hdr Ext Len, discard the packet and send an
      ICMPv6 Parameter Problem, Code 0, message to the Source Address,
      pointing to the Segments Left field.

   *  Decrement Segments Left.

   *  Search for the current SID in the CRH-FIB.  In this document, the
      "current SID" is the SID list entry referenced by the Segments
      Left field.

   *  If the search does not return a CRH-FIB entry, discard the packet
      and send an ICMPv6 Parameter Problem, Code 0, message to the
      Source Address, pointing to the current SID.

   *  If Segments Left is greater than 0 and the CRH-FIB entry contains
      a multicast address, discard the packet and send an ICMPv6
      Parameter Problem, Code 0, message to the Source Address, pointing
      to the current SID.

   *  If present, copy the IPv6 address from the CRH-FIB entry to the
      Destination Address field in the IPv6 header.

   *  Decrement the IPv6 Hop Limit.

   *  If the CRH-FIB entry contains a service function, execute it.

   *  If Segments Left is equal to zero, and the PSP flag in the CRH-FIB
      entry is set, execute the CRH removal procedure ( Section 5.2).

   *  Submit the packet, its topological function and its parameters to
      the IPv6 module.  See NOTE.

   NOTE: By default, the IPv6 module determines the next-hop and
   forwards the packet.  However, the topological function may elicit
   another behavior.  For example, the IPv6 module may forward the
   packet through a specified interface.

5.1.  Computing Minimum CRH Length

   The algorithm described in this section accepts the following CRH
   fields as its input parameters:

   *  Routing Type (i.e., CRH-16 or CRH-32).

   *  Segments Left.

   It yields L, the minimum CRH length.  The minimum CRH length is
   measured in 8-octet units, not including the first 8 octets.

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   <CODE BEGINS>
   switch(Routing Type) {
       case CRH-16:
           if (Segments Left <= 2)
               return(0)
           sidsBeyondFirstWord = Segments Left - 2;
           sidPerWord = 4;
       case CRH-32:
           if (Segments Left <= 1)
               return(0)
           sidsBeyondFirstWord = Segments Left - 1;
           sidsPerWord = 2;
       case default:
           return(0xFF);
       }

   words = sidsBeyondFirstWord div sidsPerWord;
   if (sidsBeyondFirstWord mod sidsPerWord)
       words++;

   return(words)
   <CODE ENDS>

5.2.  CRH Removal Procedure

   The processing node SHOULD execute the following procedure, if it is
   capable of doing so:

   *  Update the Next Header field in the header preceding the CRH using
      a value taken from the Next Header field in the CRH.

   *  Decrease the Payload Length filed in the IPv6 header by 8*(x+1),
      where value of x is equal to the value of the Hdr Ext Len field in
      the CRH.

   *  Remove the CRH from the IPv6 header chain.

6.  Mutability

   In the CRH, the Segments Left field is mutable.  All remaining fields
   are immutable.

7.  Applications And SIDs

   A CRH contains one or more SIDs.  Each SID is processed by exactly
   one node.

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   Therefore, a SID is not required to have domain-wide significance.
   Applications can:

   *  Allocate SIDs so that they have domain-wide significance.

   *  Allocate SIDs so that they have node-local significance.

8.  Management Considerations

   PING and TRACEROUTE [RFC2151] both operate correctly in the presence
   of the CRH.

9.  Security Considerations

   Networks that process the CRH MUST NOT accept packets containing the
   CRH from untrusted sources.  Their border routers SHOULD discard
   packets that satisfy the following criteria:

   *  The packet contains a CRH

   *  The Segments Left field in the CRH has a value greater than 0

   *  The Destination Address field in the IPv6 header represents an
      interface that resides inside of the network.

   Many border routers cannot filter packets based upon the Segments
   Left value.  These border routers MAY discard packets that satisfy
   the following criteria:

   *  The packet contains a CRH

   *  The Destination Address field in the IPv6 header represents an
      interface that resides inside of the network.

10.  Implementation and Deployment Status

   Juniper Networks has produced experimental implementations of the CRH
   on:

   *  A LINUX-based software platform

   *  The MX-series (ASIC-based) router

   Liquid Telecom has deployed the CRH, on a limited basis, in their
   network.  Other experimental deployments are in progress.

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11.  IANA Considerations

   This document makes the following registrations in the "Internet
   Protocol Version 6 (IPv6) Parameters" "Routing Types" subregistry
   maintained by IANA:

            +-------+------------------------------+---------------+
            | Value | Description                  | Reference     |
            +=======+==============================+===============+
            | 5     | CRH-16                       | This document |
            +-------+------------------------------+---------------+
            | 6     | CRH-32                       | This document |
            +-------+------------------------------+---------------+

12.  Acknowledgements

   Thanks to Dr. Vanessa Ameen, Fernando Gont, Naveen Kottapalli, Joel
   Halpern, Tony Li, Gerald Schmidt, Nancy Shaw, Ketan Talaulikar, and
   Chandra Venkatraman for their contributions to this document.

13.  Contributors

      Gang Chen

      Baidu

      No.10 Xibeiwang East Road Haidian District

      Beijing 100193 P.R.  China

      Email: phdgang@gmail.com

      Yifeng Zhou

      ByteDance

      Building 1, AVIC Plaza, 43 N 3rd Ring W Rd Haidian District

      Beijing 100000 P.R.  China

      Email: yifeng.zhou@bytedance.com

      Gyan Mishra

      Verizon

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      Silver Spring, Maryland, USA

      Email: hayabusagsm@gmail.com

14.  References

14.1.  Normative References

   [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>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [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>.

   [RFC8201]  McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
              "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
              DOI 10.17487/RFC8201, July 2017,
              <https://www.rfc-editor.org/info/rfc8201>.

14.2.  Informative References

   [IANA-RH]  IANA, "Routing Headers",
              <https://www.iana.org/assignments/ipv6-parameters/
              ipv6-parameters.xhtml#ipv6-parameters-3>.

   [ISO10589-Second-Edition]
              International Organization for Standardization,
              ""Intermediate system to Intermediate system intra-domain
              routeing information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode Network Service (ISO 8473)", ISO/IEC
              10589:2002, Second Edition,", November 2001.

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   [RFC2151]  Kessler, G. and S. Shepard, "A Primer On Internet and TCP/
              IP Tools and Utilities", FYI 30, RFC 2151,
              DOI 10.17487/RFC2151, June 1997,
              <https://www.rfc-editor.org/info/rfc2151>.

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

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6890]  Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
              "Special-Purpose IP Address Registries", BCP 153,
              RFC 6890, DOI 10.17487/RFC6890, April 2013,
              <https://www.rfc-editor.org/info/rfc6890>.

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

Appendix A.  CRH Processing Examples

   This appendix demonstrates CRH processing in the following scenarios:

   *  The SID list contains one entry for each segment in the path
      (Appendix A.1).

   *  The SID list omits the first entry in the path (Appendix A.2).

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    -----------                 -----------                 -----------
   |Node: S    |               |Node: I1   |               |Node: I2   |
   |Loopback:  |---------------|Loopback:  |---------------|Loopback:  |
   |2001:db8::a|               |2001:db8::1|               |2001:db8::2|
    -----------                 -----------                 -----------
         |                                                       |
         |                      -----------                      |
         |                     |Node: D    |                     |
          ---------------------|Loopback:  |---------------------
                               |2001:db8::b|
                                -----------

                        Figure 3: Reference Topology

   Figure 3 provides a reference topology that is used in all examples.

                +=====+==============+===================+
                | SID | IPv6 Address | Forwarding Method |
                +=====+==============+===================+
                | 2   | 2001:db8::2  | Least-cost path   |
                +-----+--------------+-------------------+
                | 11  | 2001:db8::b  | Least-cost path   |
                +-----+--------------+-------------------+

                            Table 1: Node SIDs

   Table 1 describes two entries that appear in each node's CRH-FIB.

A.1.  The SID List Contains One Entry For Each Segment In The Path

   In this example, Node S sends a packet to Node D, via I2.  In this
   example, I2 appears in the CRH segment list.

        +=====================================+===================+
        | As the packet travels from S to I2: |                   |
        +=====================================+===================+
        | Source Address = 2001:db8::a        | Segments Left = 1 |
        +-------------------------------------+-------------------+
        | Destination Address = 2001:db8::2   | SID[0] = 11       |
        +-------------------------------------+-------------------+
        |                                     | SID[1] = 2        |
        +-------------------------------------+-------------------+

                                  Table 2

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        +=====================================+===================+
        | As the packet travels from I2 to D: |                   |
        +=====================================+===================+
        | Source Address = 2001:db8::a        | Segments Left = 0 |
        +-------------------------------------+-------------------+
        | Destination Address = 2001:db8::b   | SID[0] = 11       |
        +-------------------------------------+-------------------+
        |                                     | SID[1] = 2        |
        +-------------------------------------+-------------------+

                                  Table 3

A.2.  The SID List Omits The First Entry In The Path

   In this example, Node S sends a packet to Node D, via I2.  In this
   example, I2 does not appear in the CRH segment list.

        +=====================================+===================+
        | As the packet travels from S to I2: |                   |
        +=====================================+===================+
        | Source Address = 2001:db8::a        | Segments Left = 1 |
        +-------------------------------------+-------------------+
        | Destination Address = 2001:db8::2   | SID[0] = 11       |
        +-------------------------------------+-------------------+

                                  Table 4

        +=====================================+===================+
        | As the packet travels from I2 to D: |                   |
        +=====================================+===================+
        | Source Address = 2001:db8::a        | Segments Left = 0 |
        +-------------------------------------+-------------------+
        | Destination Address = 2001:db8::b   | SID[0] = 11       |
        +-------------------------------------+-------------------+

                                  Table 5

Appendix B.  A Packet Recycling Use-Case

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                Network A--D1
               /     \     /
              /       \   /
             /         \ /
   S  ----  P           +
             \        /  \
              \      /    \
               \    /      \
                Network B---DN

                    Figure 4: Packet Recycling Use-case

   In Figure 4:

   *  The SR domain contains Node S, Node P, and a set of destination
      nodes (D1 through DN)

   *  S is connected to P

   *  P is connected to Network A and to Network B.  Neither of these
      networks are SR-capable.

   *  The destination nodes connect to both Network A and Network B

   S needs to reach each destination node through two SR paths.  One SR
   path traverses Network A while the other traverses Network B.

   Uncompressed SRv6 can encode this SR Path in two segments,with one
   segment instantiated on P and the other on the destination.  To
   support this strategy, P instantiates two END.X SIDs (one per
   network).

   CRH compressed SRv6 can encode this SR Path in two or three segments.
   When it encodes the path in two segments, one segment instantiated on
   P and the other on the destination.  To support this strategy, P
   instantiates 2*N SIDs (one per network per destination).  When CRH
   compressed SRv6 encodes the path in three segments, two segments are
   instantiated on P and the other on the destination.  The first
   segment on P updates the IPv6 Destination address without forwarding
   the packet, while the other segment on P forwards the packet without
   updating the IPv6 destination address.  To support this strategy, P
   instantiates 2+N SIDs (one per network and one per destination).

Authors' Addresses

   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive

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   Herndon, Virginia 20171
   United States of America

   Email: rbonica@juniper.net

   Yuji Kamite
   NTT Communications Corporation
   3-4-1 Shibaura, Minato-ku,
   108-8118
   Japan

   Email: y.kamite@ntt.com

   Andrew Alston
   Liquid Telecom
   Nairobi
   Kenya

   Email: Andrew.Alston@liquidtelecom.com

   Daniam Henriques
   Liquid Telecom
   Johannesburg
   South Africa

   Email: daniam.henriques@liquidtelecom.com

   Luay Jalil
   Verizon
   Richardson, Texas
   United States of America

   Email: luay.jalil@one.verizon.com

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