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6man                                                           R. Bonica
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                       February 27, 2019
Expires: August 31, 2019


                The IPv6 Compressed Routing Header (CRH)
                   draft-bonica-6man-comp-rtg-hdr-00

Abstract

   This document defines the Compressed Routing Header (CRH).  The CRH,
   like any other Routing header, contains a list of segment identifiers
   (SID).  The CRH differs from other Routing headers in that its
   segment identifiers can be 8, 16 or 32 bits long.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 31, 2019.

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
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   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.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  The Compressed Routing Header (CRH) . . . . . . . . . . . . .   3
   4.  Segment Identifiers (SID) . . . . . . . . . . . . . . . . . .   6
   5.  Processing Rules  . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  CRH Specific  . . . . . . . . . . . . . . . . . . . . . .   7
       5.2.1.  Computing Minimum CRH Length  . . . . . . . . . . . .   8
   6.  Mutability  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Management Considerationsinclude  . . . . . . . . . . . . . .   9
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  CRH Processing Examples  . . . . . . . . . . . . . .  11
     A.1.  Loose Source Routing  . . . . . . . . . . . . . . . . . .  13
     A.2.  Loose Source Routing Preserving The First SID . . . . . .  13
     A.3.  Strict Source Routing . . . . . . . . . . . . . . . . . .  14
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   An IPv6 [RFC8200] source node can steer a packet through a specific
   path to its destination.  The source node defines the path as an
   ordered list of segments and encodes the path in an IPv6 Routing
   header.  As per [RFC8200], all Routing headers includes the following
   fields:

   o  Next Header - Identifies the header immediately following the
      Routing header.

   o  Hdr Ext Len - Length of the Routing header.

   o  Routing Type - Identifies the particular Routing header variant.

   o  Segments Left - The number of segments still to be traversed
      before reaching the destination.

   o  Type-specific Data - Syntax and semantics are defined by the
      Routing Type.

   The following Routing types are currently defined:

   o  Source Route (i.e., RH0) [RFC5095] (deprecated)



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   o  Type 2 Routing Header [RFC6275]

   o  RPL Source Route Header [RFC6554]

   o  Segment Routing Header (SRH)
      [I-D.ietf-6man-segment-routing-header]

   In each of the above-mentioned Routing Types, Type-specific Data
   contains a list of one or more segment identifiers (SID).  Typically,
   a SID is an IPv6 address that identifies a segment endpoint.  In the
   SRH, the SID may carry additional semantics.

   In all cases, the SID is 128 bits long.  Therefore, routing headers
   can be very large.  For example, an 88-byte Source Route header is
   required to specify a path that contains six segments.  The same can
   be said of the SRH.

   Large Routing headers are undesirable for the following reasons:

   o  Many ASIC-based forwarders copy the entire IPv6 extension header
      chain from buffer memory to on-chip memory.  As the size of the
      IPv6 extension header chain increases, so does the cost of this
      copy.

   o  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 becomes
      pronounced.

   This document defines the Compressed Routing Header (CRH).  The CRH,
   like any other Routing header, contains a list of SIDs.  The CRH
   differs from other Routing headers in that its SIDs can be 8, 16, or
   32 bits long.

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 Header (CRH)

   Figure 1 depicts the CRH.





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


                 Figure 1: Compressed Routing Header (CRH)

   The CRH contains the following fields:

   o  Next Header - Defined in [RFC8200].

   o  Hdr Ext Len - Defined in [RFC8200].

   o  Routing Type - Defined in [RFC8200].  Value TBD by IANA.

   o  Segments Left (SL) - Defined in [RFC8200].

   o  Segments - 6-bit unsigned integer.  Represents the number of
      entries in the SID List.

   o  Com (Compression) - 2 bits.  Represents the length of each entry
      in the SID List.  Values are eight bits (0), sixteen bits (1),
      thirty-two bits (2), and reserved (3).

   o  Reserved - SHOULD be set to zero by the sender.  MUST be ignored
      by the receiver.

   o  SID List - An zero-indexed list of SIDs.  SIDs are listed in
      reverse order, with SID[0] representing the packet's ultimate
      destination, SID[1] representing the previous segment endpoint and
      so forth.  See Section 4 for SID details.

   Figure 2 through Figure 4 illustrate CRH encodings with Com equal to
   0, 1 and 2.  In all cases, the CRH MUST end on a 64-bit boundary.
   Therefore, the CRH MAY be padded with zeros.










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


                Figure 2: Eight-bit Encoding (Com equals 0)

        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 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Segments |Com|                  Reserved                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             SID[0]            |          SID[1]               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
       |                          .........
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-



               Figure 3: Sixteen-bit Encoding (Com equals 1)

       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 |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Segments |Com|                  Reserved                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +                             SID[0]                            +
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +                             SID[1]                            +
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                                                              //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      +                             SID[n]                            +
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 4: Thirty-two bit Encoding (Com equals 2)




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4.  Segment Identifiers (SID)

   This document defines the following SID types:

   o  Loosely routed

   o  Strictly routed

   All SIDs, regardless of type, map to exactly one IPv6 address.  The
   mapped address identifies an interface or set of interfaces (in the
   case of multicast) that terminate the segment.  The address MUST be
   one of the following:

   o  A globally scoped IPv6 unicast address [RFC4291].

   o  A Unique Local IPv6 Unicast Address (ULA) [RFC4193].

   o  A Multicast address [RFC4291].

   A strictly routed SID also maps to a link interface.  Nodes send
   packets through that interface in order to access the segment
   endpoint.

   SIDs are instantiated on nodes and their significance is limited to
   the node upon which they are instantiated.  For example, assume that
   a SID is instantiated on multiple nodes.  It can be loosely routed on
   one node and strictly routed on another.  Likewise, it can map to a
   different globally scoped address on each node.  See Appendix A for
   an example.

   Forwarding nodes can learn the above-mentioned mappings from a
   central controller, from a distributed routing protocol or using any
   other means.  The mechanisms that forwarding nodes use to learn the
   above-mentioned mappings are beyond the scope of this document.

5.  Processing Rules

5.1.  General

   [RFC8200] defines rules that apply to IPv6 extension headers, in
   general, and IPv6 Routing headers, in particular.  All of these rules
   apply to the CRH.

   For example:

   o  Extension headers (except for the Hop-by-Hop Options header) are
      not processed, inserted, or deleted by any node along a packet's
      delivery path, until the packet reaches the node (or each of the



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      set of nodes, in the case of multicast) identified in the
      Destination Address field of the IPv6 header.

   o  If, while processing a received packet, a node encounters a
      Routing header with an unrecognized Routing Type value, the
      required behavior of the node depends on the value of the Segments
      Left field.  If Segments Left is zero, the node must ignore the
      Routing header and proceed to process the next header in the
      packet, whose type is identified by the Next Header field in the
      Routing header.  If Segments Left is non-zero, the node must
      discard the packet and send an ICMP [RFC4443] Parameter Problem,
      Code 0, message to the packet's Source Address, pointing to the
      unrecognized Routing Type.

   o  If, after processing a Routing header of a received packet, an
      intermediate node determines that the packet is to be forwarded
      onto a link whose link MTU is less than the size of the packet,
      the node must discard the packet and send an ICMP Packet Too Big
      message to the packet's Source Address.

5.2.  CRH Specific

   When a node recognizes and processes a CRH, it executes the following
   procedure:

   o  If the IPv6 Source Address is a link-local address, discard the
      packet.

   o  If the IPv6 Source Address is a multicast address, discard the
      packet.

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

   o  If Segments Left is greater than Segments, send an ICMP Parameter
      Problem, Code 0, message to the Source Address, pointing to the
      Segments Left field, and discard the packet.

   o  If Com is equal to (3) Reserved, send an ICMP Parameter Problem,
      Code 0, message to the Source Address, pointing to the Com field,
      and discard the packet.

   o  If the IPv6 Hop Limit is less than or equal to 1, send an ICMP
      Time Exceeded -- Hop Limit Exceeded in Transit message to the
      Source Address and discard the packet.

   o  Compute L, the minimum CRH length (See Section 5.2.1)




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

   o  Decrement Segments Left (i.e., SL).

   o  Search for SID[SL] in the table that maps SID's to IPv6 addresses
      and interfaces.  If SID[SL] cannot be found in that table, send an
      ICMP Parameter Problem, Code 0, message to the Source Address,
      pointing to SID[SL], and discard the packet.

   o  Copy the address associated with SID[SL] to the IPv6 Destination
      Address.

   o  If the IPv6 Destination address is a multicast address and SL is
      greater than zero, send an ICMP Parameter Problem, Code 0, message
      to the Source Address, pointing to Segment List [SL], and discard
      the packet.

   o  Decrement the IPv6 Hop Limit.

   o  If SID[SL] is a loosely routed segment, resubmit the packet to the
      IPv6 module for transmission to the new destination.

   o  If SID[SL] is a strictly routed segment, forward the packet
      through the interface that is associated with SID[SL].

   The above stated rules are demonstrated in Appendix A.

5.2.1.  Computing Minimum CRH Length

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

   o  Compression (Com).

   o  Segments.

   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>

           if (Com == 0 ) {         /* Eight bit encoding */
               L = ( Segments / 8 );
               if ( Segments % 8 )
                   L++;
               }
           elsif (Com == 1 ) {    /* Sixteen bit encoding */
               L = ( Segments / 4 );
               if ( Segments % 4 )
                   L++;
               }
           elsif (Com == 2 ) {    /* Thirty-two bit encoding */
               L = ( Segments / 2 );
               if ( Segments % 2 )
                   L++;
               }
           else {                  /* Invalid Com */
               L = 0xFF

               }

           return(L)

           <CODE ENDS>


6.  Mutability

   The Segments Left field is mutable and MAY be decremented by
   processing nodes.  All remaining fields are immutable.

7.  Management Considerationsinclude

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

8.  Security Considerations

   The CRH can be used within trusted domains only.  In order to enforce
   this requirement, domain edge routers MUST do one of the following:

   o  Discard all inbound packets that contain a CRH

   o  Authenticate [RFC4302] [RFC4303] all inbound packets that contain
      a CRH





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9.  IANA Considerations

   This document makes the following registration in the Internet
   Protocol Version 6 (IPv6) Parameters "Routing Type" registry
   maintained by IANA:

        Value            Description                 Reference
      ------------------------------------------------------------
        TBD      Compressed Routing Header (CRH)     This document

10.  Acknowledgements

   Thanks to Joel Halpern, Gerald Schmidt, Nancy Shaw and Chandra
   Venkatraman for their comments.

11.  References

11.1.  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>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <https://www.rfc-editor.org/info/rfc4302>.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [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>.






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   [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>.

11.2.  Informative 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.

   [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>.

   [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>.

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095,
              DOI 10.17487/RFC5095, December 2007,
              <https://www.rfc-editor.org/info/rfc5095>.

   [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
              Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
              2011, <https://www.rfc-editor.org/info/rfc6275>.

   [RFC6554]  Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
              Routing Header for Source Routes with the Routing Protocol
              for Low-Power and Lossy Networks (RPL)", RFC 6554,
              DOI 10.17487/RFC6554, March 2012,
              <https://www.rfc-editor.org/info/rfc6554>.

Appendix A.  CRH Processing Examples

   This appendix provides examples of CRH processing in the following
   applications:

   o  Loose source routing (Appendix A.1)



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   o  Loose source routing preserving the first SID (Appendix A.2)

   o  Strict source routing (Appendix A.3)

                                -----------
            2001:db8:0:2/64    |Node: I2   |   2001:db8:0:4/64
         ----------------------|Loopback:  |--------------------
        |                  ::2 |2001:db8::2| ::1                |
        |                       -----------                     |
        | ::1                                               :: 2|
    -----------                 -----------                 -----------
   |Node: S    |2001:db8:0:1/64|Node: I1   |2001:db8:0:3/64|Node: I3   |
   |Loopback   |---------------|Loopback:  |---------------|Loopback:  |
   |2001:db8::a| ::1       ::2 |2001:db8::1| ::1       ::2 |2001:db8::3|
    -----------                 -----------                 -----------
                                                                 | ::1
                                -----------                      |
                               |Node: D    |   2001:db8:0:b/64   |
                               |Loopback:  |---------------------
                               |2001:db8::b| ::2
                                -----------

                       Figure 5: Reference Topology

   Figure 5 provides a reference topology that is used in all examples.

                +--------------------+-----+--------------+
                | Instantiating Node | SID | IPv6 Address |
                +--------------------+-----+--------------+
                |        All         | 1   | 2001:db8::1  |
                |        All         | 2   | 2001:db8::2  |
                |        All         | 3   | 2001:db8::3  |
                |        All         | 10  | 2001:db8::a  |
                |        All         | 11  | 2001:db8::b  |
                +--------------------+-----+--------------+

                       Table 1: Loosely Routed SIDs

   Table 1 provides mappings for loosely routed SIDs.  These mappings
   are instantiated on all nodes in the reference topology.











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        +--------------------+-----+-----------------+-----------+
        | Instantiating Node | SID |   IPv6 Address  | Interface |
        +--------------------+-----+-----------------+-----------+
        |         S          | 129 | 2001:db8:0:1::2 |  S -> I1  |
        |         S          | 130 | 2001:db8:0:2::2 |  S -> I2  |
        |         I1         | 129 | 2001:db8:0:3::2 |  I1 -> I3 |
        |         I2         | 129 | 2001:db8:0:4::2 |  I2 -> I3 |
        |         I3         | 129 | 2001:db8:0:b::2 |  I3 -> D  |
        +--------------------+-----+-----------------+-----------+

                       Table 2: Strictly Routed SIDs

   Table 2 provides mappings for strictly routed SIDs.  These mappings
   are available on the instantiating node only.

A.1.  Loose Source Routing

   In this example, Node S sends a packet to Node D, specifying loose
   source route through Node I3.  In this example, the first node in the
   path, I3, does not appear in the CRH segment list.  Therefore, the
   destination node may not be able to send return traffic through the
   same path.

        +-------------------------------------+-------------------+
        | As the packet travels from S to I3: |                   |
        +-------------------------------------+-------------------+
        | Source Address = 2001:db8::a        | Segments = 1      |
        | Destination Address = 2001:db8::3   | Segments Left = 1 |
        |                                     | SID[0] = 11       |
        +-------------------------------------+-------------------+

        +-------------------------------------+-------------------+
        | As the packet travels from I3 to D: |                   |
        +-------------------------------------+-------------------+
        | Source Address = 2001:db8::a        | Segments = 1      |
        | Destination Address = 2001:db8::b   | Segments Left = 0 |
        |                                     | SID[0] = 11       |
        +-------------------------------------+-------------------+

A.2.  Loose Source Routing Preserving The First SID

   In this example, Node S sends a packet to Node D, specifying loose
   source route through Node I3.  In this example, the first node in the
   path, I3, appears in the CRH segment list.  Therefore, the
   destination node can send return traffic through the same path.






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        +-------------------------------------+-------------------+
        | As the packet travels from S to I3: |                   |
        +-------------------------------------+-------------------+
        | Source Address = 2001:db8::a        | Segments = 2      |
        | Destination Address = 2001:db8::3   | Segments Left = 1 |
        |                                     | SID[0] = 11       |
        |                                     | SID[1] = 3        |
        +-------------------------------------+-------------------+

        +-------------------------------------+-------------------+
        | As the packet travels from I3 to D: |                   |
        +-------------------------------------+-------------------+
        | Source Address = 2001:db8::a        | Segments = 2      |
        | Destination Address = 2001:db8::b   | Segments Left = 0 |
        |                                     | SID[0] = 11       |
        |                                     | SID[1] = 3        |
        +-------------------------------------+-------------------+

A.3.  Strict Source Routing

   In this example, Node S sends a packet to Node D, specifying the
   strict source route through I1 and I3.

       +---------------------------------------+-------------------+
       | As the packet travels from S to I1:   |                   |
       +---------------------------------------+-------------------+
       | Source Address = 2001:db8::a          | Segments = 2      |
       | Destination Address = 2001:db8:0:1::2 | Segments Left = 2 |
       |                                       | SID[0] = 129      |
       |                                       | SID[1] = 129      |
       +---------------------------------------+-------------------+

       +---------------------------------------+-------------------+
       | As the packet travels from I1 to I3:  |                   |
       +---------------------------------------+-------------------+
       | Source Address = 2001:db8::a          | Segments = 2      |
       | Destination Address = 2001:db8:0:3::2 | Segments Left = 1 |
       |                                       | SID[0] = 129      |
       |                                       | SID[1] = 129      |
       +---------------------------------------+-------------------+











Bonica                   Expires August 31, 2019               [Page 14]


Internet-Draft       IPv6 Compressed Routing Header        February 2019


       +---------------------------------------+-------------------+
       | As the packet travels from I3 to D:   |                   |
       +---------------------------------------+-------------------+
       | Source Address = 2001:db8::a          | Segments = 2      |
       | Destination Address = 2001:db8:0:b::2 | Segments Left = 0 |
       |                                       | SID[0] = 129      |
       |                                       | SID[1] = 129      |
       +---------------------------------------+-------------------+

Author's Address

   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia  20171
   USA

   Email: rbonica@juniper.net

































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