Compressed Routing Header (CRH) Helper Option
draft-bonica-6man-crh-helper-opt-04

Document Type Active Internet-Draft (individual)
Authors Xing Li  , Congxiao Bao  , Eddie Ruan  , Ron Bonica 
Last updated 2021-10-11
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6man WG                                                            X. Li
Internet-Draft                                                    C. Bao
Intended status: Standards Track       CERNET Center/Tsinghua University
Expires: 14 April 2022                                           E. Ruan
                                                           Fungible Inc.
                                                               R. Bonica
                                                        Juniper Networks
                                                         11 October 2021

             Compressed Routing Header (CRH) Helper Option
                  draft-bonica-6man-crh-helper-opt-04

Abstract

   This document defines the IPv6 Compressed Routing Header (CRH) Helper
   option.  When a source node sends a packet with a CRH, it can use the
   CRH Helper option to provide additional information to downstream
   nodes.

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 14 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Option Format . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Option Processing . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   IPv6 [RFC8200] source nodes use the Compressed Routing Header (CRH)
   [I-D.bonica-6man-comp-rtg-hdr] to steer packets along a delivery path
   to their destination.  Two CRH versions have been defined.  The
   CRH-16 encodes segment endpoints in 16 bits, while CRH-32, encodes
   segment endpoints in 32 bits.

   Both CRH versions contain the following fields:

   *  Next Header - Identifies the header immediately following the CRH.

   *  Hdr Ext Len - Length of the CRH.

   *  Routing Type - Identifies the Routing header variant (i.e., CRH-16
      or CRH-32).

   *  Segments Left - The number of segments still to be traversed
      before reaching the packet's ultimate destination.

   *  Segment Identifier (SID) List - Represents the delivery path as an
      ordered list of Segment Identifiers (SID).  SIDs are listed in
      reverse order, with SID[0] representing the final segment, SID[1]
      representing the penultimate segment, and so forth.  SIDs are
      listed in reverse order so that Segments Left can be used as an
      index to the SID List.  The SID indexed by Segments Left is called
      the current SID.

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   As per [RFC8200], when an IPv6 node receives a packet, it examines
   the packet's destination address.  If the destination address
   represents an interface belonging to the node, the node processes the
   next header.  If the next header is a CRH, it is processed as
   follows:

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

   *  Decrement Segments Left.

   *  Query a local data structure, called the CRH Forwarding
      Information Base (CRH-FIB), searching for an entry that is indexed
      by the current SID.

   *  If the above-mentioned query returns a CRH-FIB entry, update the
      packet's IPv6 Destination Address and forward the packet.

   In a typical CRH deployment, every segment ingress node maintains a
   complete CRH-FIB and the above-mentioned query returns a CRH-FIB
   entry.  However, in some CRH deployments, some segment ingress nodes
   maintain a complete CRH-FIB while others do not.  For example, a node
   that does not participate in a control plane or communicate with a
   controller may not maintain a CRH-FIB.

   This document defines the IPv6 CRH Helper option.  When a source node
   sends a packet with a CRH, it can use the IPv6 CRH Helper option to
   provide CRH-FIB information to downstream nodes that do not maintain
   a complete CRH-FIB.

   If a segment ingress node queries its CRH-FIB, searching for an entry
   that is indexed by the current SID, and that query returns nothing,
   the segment ingress node can obtain the required CRH-FIB information
   from the IPv6 CRH Helper option.  If the segment ingress node cannot
   obtain the required CRH-FIB information from either source, it
   discards the packet and sends an ICMPv6 [RFC4443] Parameter Problem
   message to the source node.

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.

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3.  Option Format

   The CRH Helper option contains the following fields:

   *  Option Type - (8-bits) CRH Helper option.  Value TBD by IANA.
      (Suggested value: 0x11).  See Note below.

   *  Opt Data Len - (8-bits) Length of the option, in octets, excluding
      the Option Type and Option Length fields.

   *  Helper List - (Variable length) A list of Helpers.

   Each Helper contains the following fields:

   *  Helper Length - (8-bits) Length of the Helper, in octets,
      excluding Helper Length.  Value MUST be greater than 2 and less
      than 19.

   *  Low SID - (8-bits) Index to the CRH SID List.  References the
      first member of the SID List to which this Helper applies.

   *  High SID - (8-bits) Index to the CRH SID List.  References the
      last member of the SID List to which this Helper applies.

   *  Prefix field (variable length): An IPv6 Prefix.

   NOTE : The highest-order two bits of the Option Type (i.e., the "act"
   bits) are 00.  These bits specify the action taken by a destination
   node that does not recognize the option.  The required action is to
   skip over this option and continue processing the header.

   The third highest-order bit of the Option Type (i.e., the "chg" bit)
   is 0.  This indicates that Option Data cannot be modified along the
   path between the packet's source and its destination.

4.  Option Processing

   When a segment endpoint node processes a CRH, it attempts to resolve
   the SID using information contained by its CRH-FIB.  If it cannot
   resolve the SID using CRH-FIB, it attempts to resolve the SID using
   information received in an applicable Helper.  If no Helper applies
   to the current SID, the processing node discards the packet and sends
   an ICMPv6 Parameter Problem message to the source node.

   When the processing node uses a Helper to resolve a SID, it executes
   the following procedure:

   *  Set the IPv6 Destination Address to 0::

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   *  Overwrite the low order bits of the IPv6 Destination Address with
      the current SID found in the CRH

   *  Overwrite the high order bits of the IPv6 Destination Address with
      the prefix found in the applicable Helper

   If the prefix found in the applicable Helper is 16 bytes long, it
   overwrites the entire IPv6 Destination Address.

   The CRH Helper option MAY occur in a Destination Options header that
   precedes a CRH.  It SHOULD NOT occur in a Hop-by-hop options header
   or in a Destination Options header that precedes an upper-layer
   header.

   When a segment ingress node resolves a SID using information obtained
   from the CRH helper option, it forwards the packet through the least-
   cost path to its new destination.

   Information obtained from the CRH Helper option is transient.  It is
   discarded as soon as the packet that carried it has been processed.

5.  Security Considerations

   When a segment endpoint node processes a CRH, it attempts to resolve
   the SID using information contained by its CRH-FIB.  If it can
   resolve the SID using CRH-FIB, it MUST ignore the CRH Helper option,
   even if it contains an applicable Helper.

6.  IANA Considerations

   IANA is requested to allocate a code point from the Destination
   Options and Hop-by-hop Options registry
   (https://www.iana.org/assignments/ipv6-parameters/
   ipv6-parameters.xhtml#ipv6-parameters-2).  This option is called "CRH
   Helper Option".  The "act" bits are 00 and the "chg" bit is 0.
   (Suggested value: 0x11).

7.  Acknowledgements

   Thanks to TBD for their careful review of this document.

8.  Normative References

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   [I-D.bonica-6man-comp-rtg-hdr]
              Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L.
              Jalil, "The IPv6 Compact Routing Header (CRH)", Work in
              Progress, Internet-Draft, draft-bonica-6man-comp-rtg-hdr-
              26, 25 May 2021, <https://www.ietf.org/archive/id/draft-
              bonica-6man-comp-rtg-hdr-26.txt>.

   [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>.

Authors' Addresses

   Xing Li
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing
   100084
   People's Republic of China

   Email: xing@cernet.edu.cn

   Congxiao Bao
   CERNET Center/Tsinghua University
   Room 225, Main Building, Tsinghua University
   Beijing
   100084
   People's Republic of China

   Email: congxiao@cernet.edu

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   Eddie Ruan
   Fungible Inc.
   3201 Scott Blvd
   Santa Clara, California 95054
   United States of America

   Email: eddie.ruan@fungible.com

   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia 20171
   United States of America

   Email: rbonica@juniper.net

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