Inserting, Processing And Deleting IPv6 Extension Headers
draft-bonica-6man-ext-hdr-update-02

6man                                                           R. Bonica
Internet-Draft                                          Juniper Networks
Updates: RFC 8200 (if approved)                            March 9, 2020
Intended status: Standards Track
Expires: September 10, 2020

       Inserting, Processing And Deleting IPv6 Extension Headers
                  draft-bonica-6man-ext-hdr-update-02

Abstract

   This document provides guidance regarding the processing, insertion
   and deletion of IPv6 extension headers.  It updates RFC 8200.

Status of This Memo

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

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   This Internet-Draft will expire on September 10, 2020.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Updates To RFC 8200 . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Original Text . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Updated Text  . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   In IPv6 [RFC8200] optional internet-layer information is encoded in
   extension headers.  As specified by [RFC8200], "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 set of nodes, in
   the case of multicast) identified in the Destination Address field of
   the IPv6 header".

   The statement quoted above identifies nodes upon which extension
   headers are not processed, inserted or deleted.  It does not imply
   that extension headers can be processed, inserted or deleted on any
   other node along a packet's delivery path.

   This document provides guidance regarding the processing, insertion
   and deletion of IPv6 extension headers.  It clarifies the statement
   quoted above and updates [RFC8200].

2.  Terminology

   The following terms are used in this document:

   o  Source node - An IPv6 source node accepts data from an upper-layer
      protocol, prepends an IPv6 header, and sends the resulting IPv6
      packet to a destination node.

   o  Destination node - An IPv6 destination node receives an IPv6
      packet and delivers its payload to an upper-layer protocol.  If a
      packet contains a Routing header, its destination address may
      represent an interface that belongs to a node other than the
      destination node.

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   o  Delivery path - A packet's delivery path is a series of nodes that
      a packet traverses on route to its destination.  The delivery path
      includes the destination node.

   o  Segment - A segment is a series of links and nodes in a packet's
      delivery path.  An IPv6 Routing header steers packets from segment
      to segment along the delivery path.  If a packet contains a
      Routing header, its delivery path can contain multiple segments.
      If a packet does not contain a Routing header, its delivery path
      contains only one segment.

   o  Segment egress node - A segment egress node terminates a segment.
      When a packet arrives at a segment egress node, its IPv6
      Destination Address identifies an interface that belongs to the
      node.  All destination nodes are also segment egress nodes.

3.  Updates To RFC 8200

   The terms defined in Section 2 of this document should be added to
   Section 2 of [RFC8200].

   Section 3.1 of this document quotes text from [RFC8200].  That text
   should be replaced with the text contained by Section 3.2 of this
   document.

3.1.  Original Text

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

   The Hop-by-Hop Options header is not inserted or deleted, but may be
   examined or processed by any node along a packet's delivery path,
   until the packet reaches the node (or each of the set of nodes, in
   the case of multicast) identified in the Destination Address field of
   the IPv6 header.  The Hop-by-Hop Options header, when present, must
   immediately follow the IPv6 header.  Its presence is indicated by the
   value zero in the Next Header field of the IPv6 header."

3.2.  Updated Text

   Source nodes can send packets that include extension headers.
   Extension headers are not inserted by subsequent nodes along a
   packet's delivery path.

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   The Hop-by-Hop Options header, when present, must immediately follow
   the IPv6 header.  Its presence is indicated by the value zero in the
   Next Header field of the IPv6 header.

   The Hop-by-Hop Options header can be processed by any node in a
   packet's delivery path.  The following headers can be processed by
   any segment egress node, including the destination node:

   o  Destination Options header.

   o  Routing header.

   The following headers can be processed by the destination node only:

   o  The Fragment header.

   o  The Authentication header.

   o  The Encapsulating Security Payload header.

   Except for the following fields, extension headers are not modified
   by nodes along a packet's delivery path:

   o  The Segments Left field in the Routing header.

   o  Type-specific data in the Routing header, as allowed by the
      relevant Routing type specification.

   o  Option Data in the Destination Options header.

   Extension headers are not deleted by any node along a packet's
   delivery path, until the packet reaches the destination node (or each
   of the set of destination nodes, in the case of multicast).

   Extension headers can be inspected for various purposes (e.g.,
   firewall filtering) by any node along a packet's delivery path.

4.  Motivation

   The following are reasons why extension headers are not inserted by
   nodes along a packet's delivery path:

   o  MTU black holing - Many IPv6 nodes dynamically discover Path MTU
      (PMTU) [RFC8201].  Having discovered the PMTU, they send packets
      whose size approaches, but does not exceed the PMTU.  Adding an
      extension header to such a packet can cause MTU black holing.

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   o  Incompatibility with the IPv6 Authentication Header [RFC4302] -
      IPv6 Authentication header processing relies on the immutability
      of the Payload Length field in the IPv6 header.  When a node along
      a packet's delivery path inserts an extension header, it updates
      the Payload Length field in the IPv6 header.  This causes
      Authentication header processing to fail.

   o  Semantic corruption - Insertion of an extension header can change
      the meaning of a packet.

   The following are reasons why extension headers are not deleted by
   any node along a packet's delivery path, until the packet reaches the
   destination node:

   o  Incompatibility with the IPv6 Authentication Header - IPv6
      Authentication header processing relies on the immutability of the
      Payload Length field in the IPv6 header.  When a node along a
      packet's delivery path deletes an extension header, it updates the
      Payload Length field in the IPv6 header.  This causes
      Authentication header processing to fail.

   o  Semantic corruption - Deletion of an extension header can change
      the meaning of a packet.

5.  Security Considerations

   This document does not introduce any new security considerations.

6.  IANA Considerations

   This document does not request any IANA actions.

7.  Acknowledgements

   Thanks to Bob Hinden, Brian Carpenter, Tom Herbert, Fernando Gont and
   Jinmei Tatuya for their comments and review.

8.  Normative References

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

   [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>.

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   [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>.

Author's Address

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

   Email: rbonica@juniper.net

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