IPv6 maintenance Working Group (6man)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Updates: 2460 (if approved)                                    V. Manral
Intended status: Standards Track                   Hewlett-Packard Corp.
Expires: March 14, April 5, 2014                                         R. Bonica
                                                        Juniper Networks
                                                      September 10,
                                                         October 2, 2013

              Implications of Oversized IPv6 Header Chains


   The IPv6 specification allows IPv6 header chains of an arbitrary
   size.  The specification also allows options which can in turn extend
   each of the headers.  In those scenarios in which the IPv6 header
   chain or options are unusually long and packets are fragmented, or
   scenarios in which the fragment size is very small, the first
   fragment of a packet may fail to include the entire IPv6 header
   chain.  This document discusses the interoperability and security
   problems of such traffic, and updates RFC 2460 such that the first
   fragment of a packet is required to contain the entire IPv6 header

Status of this Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 14, April 5, 2014.

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   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Updates to RFC 2460  . . . . . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 12
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13

1.  Introduction

   With IPv6, optional internet-layer information is carried in one or
   more IPv6 Extension Headers [RFC2460].  Extension headers are placed
   between the IPv6 header and the upper-layer header in a packet.  The
   term "header chain" refers collectively to the IPv6 header, extension
   headers and upper-layer header occurring in a packet.  In those
   scenarios in which the IPv6 header chain is unusually long and
   packets are fragmented, or scenarios in which the fragment size is
   very small, the header chain may span multiple fragments.

   While IPv4 had a fixed maximum length for the set of all IPv4 options
   present in a single IPv4 packet, IPv6 does not have any equivalent
   maximum limit at present.  This document updates the set of IPv6
   specifications to create an overall limit on the size of the
   combination of IPv6 options and IPv6 Extension Headers that is
   allowed in a single IPv6 packet.  Namely, it updates RFC 2460 such
   that the first fragment of a fragmented datagram is required to
   contain the entire IPv6 header chain.

   It should be noted that this requirement does not preclude the use of
   large payloads but instead merely requires that all headers, starting
   from IPv6 base header and continuing up to the upper layer header
   (e.g.  TCP or the like) be present in the first fragment.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Terminology

   For the purposes of this document, the terms Extension Header, Header
   Chain, First Fragment, and Upper-layer Header are used as follows:

   Extension Header:

      Extension Headers are defined in Section 4 of [RFC2460].  As a
      result of [I-D.ietf-6man-ext-transmit], [IANA-PROTO] provides a
      list of assigned Internet Protocol Numbers and designates which of
      those protocol numbers also represent extension headers.

   First Fragment:

      An IPv6 fragment with fragment offset equal to 0.

   IPv6 Header Chain:

      The header chain contains an initial IPv6 header, zero or more
      IPv6 extension headers, and optionally, a single upper-layer
      header.  If an upper-layer header is present, it terminates the
      header chain; otherwise the "No Next Header" value (Next Header =
      59) terminates it.

      The first member of the header chain is always an IPv6 header.
      For a subsequent header to qualify as a member of the header
      chain, it must be referenced by the "Next Header" field of the
      previous member of the header chain.  However, if a second IPv6
      header appears in the header chain, as is the case when IPv6 is
      tunneled over IPv6, the second IPv6 header is considered to be an
      upper-layer header and terminates the header chain.  Likewise, if
      an Encapsulating Security Payload (ESP) header appears in the
      header chain it is considered to be an upper-layer header and it
      terminates the header chain.

   Upper-layer Header:

      In the general case, the upper-layer header is the first member of
      the header chain that is neither an IPv6 header nor an IPv6
      extension header.  However, if either an ESP header, or a second
      IPv6 header occur in the header chain, they are considered to be
      upper layer headers and they terminate the header chain.

      Neither the upper-layer payload, nor any protocol data following
      the upper-layer payload, is considered to be part of the header
      chain.  In a simple example, if the upper-layer header is a TCP
      header, the TCP payload is not part of the header chain.  In a
      more complex example, if the upper-layer header is an ESP header,
      neither the payload data, nor any of the fields that follow the
      payload data in the ESP header are part of the header chain.

4.  Motivation

   Many forwarding devices implement stateless firewalls.  A stateless
   firewall enforces a forwarding policy on packet-by-packet basis.  In
   order to enforce its forwarding policy, the stateless firewall may
   need to glean information from both the IPv6 and upper-layer headers.

   For example, assume that a stateless firewall discards all traffic
   received from an interface unless it destined for a particular TCP
   port on a particular IPv6 address.  When this firewall is presented
   with a fragmented packet, packet that is destined for a different TCP port,
   and the entire header chain is contained within the first fragment,
   the firewall discards the first fragment and allows subsequent
   fragments to pass.  Because the first fragment was discarded, the
   packet cannot be reassembled at the destination.  Insomuch as the
   packet cannot be reassembled, the forwarding policy is enforced.

   However, when the firewall is presented with a fragmented packet and
   the header chain spans multiple fragments, the first fragment does
   not contain enough information for the firewall to enforce its
   forwarding policy.  Lacking sufficient information, the stateless
   firewall either forwards or discards that fragment.  Regardless of
   the action that it takes, it may fail to enforce its forwarding

5.  Updates to RFC 2460

   When a host fragments a IPv6 datagram, it MUST include the entire
   header chain in the first fragment.

   A host that receives a first-fragment that does not satisfy the
   above- stated requirement SHOULD discard the packet (e.g., including
   a configuration option that packet, allows such fragments to be accepted for
   backwards compatibility) and also MAY SHOULD send an ICMPv6 error message to
   the source address of the offending packet (subject to the rules for
   ICMPv6 errors specified in [RFC4443]).

   Likewise, an intermediate system (e.g. router, firewall) that
   receives an IPv6 first-fragment that does not satisfy the above-
   stated requirements MAY discard that packet, and MAY send an ICMPv6
   error message to the source address of the offending packet (subject
   to the rules for ICMPv6 error messages specified in [RFC4443]).
   Intermediate systems having this capability SHOULD support
   configuration (e.g. enable/disable) of whether such packets are
   dropped or not by the intermediate system.

   If a host or intermediate system discards a first-fragment because it
   does not satisfy the above-stated requirements, and sends an ICMPv6
   error message due to the discard, then the ICMPv6 error message MUST
   be Type 4 ("Parameter Problem") and MUST use Code TBD ("First-
   fragment has incomplete IPv6 Header Chain").  The Pointer field
   contained by the ICMPv6 Parameter Problem message MUST be set to
   zero.  Whether a host or intermediate system originates this ICMP
   message, its format is identical.

   As a result of the above mentioned requirements, a packet's header
   chain length cannot exceed the Path MTU associated with its
   destination.  Hosts MAY discover the Path MTU, using procedures such
   as those defined in [RFC1981] and [RFC4821].  However, if a host does
   not discover the Path MTU, it MUST limit the header chain length to
   1280 bytes.  Limiting the header chain length to 1280 bytes ensures
   that the header chain length does not exceed the IPv6 minimum MTU. MTU

6.  IANA Considerations

   IANA is requested to add a the following entry to the "Reason Code"
   registry for ICMPv6 "Type 4 - Parameter Problem" messages:

       TBD     IPv6 first-fragment has incomplete IPv6 header chain

7.  Security Considerations

   This document describes how improperly-fragmented packets can prevent
   traditional stateless packet filtering.

   This document updates RFC 2460 such that those packets are forbidden,
   thus enabling stateless packet filtering for IPv6.

   This specification allows nodes that drop the aforementioned packets
   to signal such packet drops with ICMPv6 "Parameter Problem, IPv6
   first-fragment has incomplete IPv6 header chain" (Type 4, Code TBD)
   error messages.

   As with all ICMPv6 error/diagnostic messages, deploying Source
   Address Forgery Prevention filters helps reduce the chances of an
   attacker successfully performing a reflection attack by sending
   forged illegal packets with the victim/target's IPv6 address as the
   IPv6 Source Address of the illegal packet [RFC2827] [RFC3704].

   A firewall that performs stateless deep packet inspection (i.e.,
   examines application payload content) might still be unable to
   correctly process fragmented packets, even if the IPv6 header chain
   is not fragmented.

8.  Acknowledgements

   The authors of this document would like to thank Ran Atkinson for
   contributing text and ideas that were incorporated into this

   The authors would like to thank (in alphabetical order) Ran Atkinson,
   Fred Baker, Brian Carpenter, Dominik Elsbroek, Wes George, Mike
   Heard, Bill Jouris, Suresh Krishnan, Dave Thaler, Ole Troan, and Eric
   Vyncke, for providing valuable comments on earlier versions of this

9.  References

9.1.  Normative References

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, August 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, "Internet Control
              Message Protocol (ICMPv6) for the Internet Protocol
              Version 6 (IPv6) Specification", RFC 4443, March 2006.

   [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
              Discovery", RFC 4821, March 2007.

              Carpenter, B. and S. Jiang, "Transmission and Processing
              of IPv6 Extension Headers",
              draft-ietf-6man-ext-transmit-04 (work in progress),
              September 2013.

9.2.  Informative References

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, March 2004.

              Internet Assigned Numbers Authority, "Protocol Numbers",
              February 2013, <http://www.iana.org/assignments/

Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com

   Vishwas Manral
   Hewlett-Packard Corp.
   191111 Pruneridge Ave.
   Cupertino, CA  95014

   Phone: 408-447-1497
   Email: vishwas.manral@hp.com

   Ronald P. Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, VA  20171

   Phone: 571 250 5819
   Email: rbonica@juniper.net