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: May 9, January 16, 2014                                      R. Bonica
                                                        Juniper Networks
                                                           July 15, 2013                                    November 5, 2012

  Security and Interoperability

              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 May 9, 2013. January 16, 2014.

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   Copyright (c) 2012 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.  Terminology  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . .  4
   3.  Interoperability Implications of Oversized IPv6 Header
       Chains . . . . . . . . . . . . . . . . . . . .  5
   4.  Motivation . . . . . . . .  5
   4.  Forwarding Implications of Oversized IPv6 Header Chains . . .  6
   5.  Security Implications of Oversized IPv6 Header Chains . . . .  7
   6.  Updating . . . . . . . . . . .  6
   5.  Updates to RFC 2460  . . . . . . . . . . . . . . . . . . . . . .  8
   7.  7
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   8.  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   9.  9
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   10. 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . 12
     10.2. . 11
     9.2.  Informative References . . . . . . . . . . . . . . . . . 12 . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 12

1.  Introduction

   With IPv6, IPv6 options are optional internet-layer information is carried inside in one or
   more IPv6 Extension Headers [RFC2460].  A sequence of more than one IPv6  Extension
   Headers headers are placed
   between the IPv6 header and the upper-layer header in a row is commonly called an "IPv6 Header Chain". 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 first fragment of a packet may fail to include the
   entire IPv6 header chain. 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
   e.g.  IPv6 jumbo 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

2.  Terminology  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

   Extension Headers:
      Any Header:

      Extension Headers as described are defined in Section 4 of [RFC2460], and
      specified in [RFC2460].
      Currently, six extension header types are defined.  [RFC2460] or any subsequent documents.

   Entire IPv6
      defines the hop-by-hop, routing, fragment and destination options
      extension header chain:
      All protocol headers types.  [RFC4302] defines the authentication
      header type and [RFC4303] defines the encapsulating security
      payload (ESP) header type.

   First Fragment:

      An IPv6 fragment with fragment offset equal to 0.

   IPv6 Header Chain:

      The initial portion of an IPv6 datagram containing headers,
      starting from the fixed IPv6 header up to (and including) the
      upper layer protocol header (TCP, UDP, etc. -- assuming there is
      one of those), including any intermediate IPv6 extension headers.

         Note: If there is an upper layer header, only the
      For a header (and
         not its payload) are considered part to qualify as a member of the "entire IPv6 header
         chain".  For example, if chain, it must
      be referenced by the upper layer protocol is TCP, only "Next Header" field of the TCP header (and not its possible data bytes) should be
         considered part previous member of
      the "entire IPv6 header chain".

3.  Interoperability Implications chain.

   Upper-layer Header:

      The first member of Oversized IPv6 Header Chains

   Some transition technologies, such as NAT64 [RFC6146], might need to
   have access to the entire IPv6 header chain in order to associate that is neither an
   incoming IPv6 packet with
      header nor an ongoing "session". IPv6 extension header.  For instance, Section 3.4 the purposes of [RFC6146] states that "The NAT64 MAY
      require that the UDP, TCP, or ICMP header this
      document, ICMPv6 is considered to be completely contained
      within an upper-layer protocol, even
      though ICMPv6 operates at the fragment that contains fragment offset equal to zero".

   Failure to include same layer as IPv6.  Also for the entire IPv6 header chain in
      purposes of this document, the first-fragment
   might cause first 32 bits of the ICMPv6 message
      (i.e., the translation function type, code fields and checksum fields) are considered
      to fail, with be the corresponding
   packets being dropped.

4.  Forwarding Implications of Oversized IPv6 Header Chains

   A lot ICMPv6 header.

         The upper-layer payload is not part of the switches upper-layer header
         and Routers in the internet do hardware based
   forwarding.  To be able to achieve a level of throughput, there therefore, is a
   fixed maximum number not part of clock cycles dedicated to each packet.
   However with the use IPv6 header chain.  For
         example, if the upper-layer protocol is TCP, the TCP payload is
         not part of unlimited options and the TCP header interleaving,
   larger packets with or the IPv6 header chain.

         When a lot of interleaving might have packet contains an ESP header [RFC4303], such header is
         considered to be forwarded
   to the software.  This is one reason why last header in the maximum size IPv6 header chain.  For
         the sake of valid
   packets with interleaved headers needs to be limited.

5. clarity, we note that only the Security Implications Parameters
         Index (SPI) and the Sequence Number fields (i.e., the first 64
         bits of Oversized IPv6 Header Chains

   Most firewalls enforce their filtering policy based on the following

   o  Source IP address

   o  Destination IP address

   o  Protocol type (e.g.  ICMPv6, TCP, UDP, SCTP)

   o  Transport-layer Source Port number

   o  Transport-layer Destination Port number

   Some firewalls reassemble fragmented packets before applying a
   filtering policy, ESP packet) are part of the ESP header (i.e., the
         Payload Data and thus always have trailer are NOT part of the aforementioned information
   available when deciding whether to allow or block a packet.  However,
   other ESP header).

4.  Motivation

   Many forwarding devices implement stateless firewalls.  A stateless firewalls (generally prevalent
   firewall enforces a forwarding policy on small/ home office
   equipment) do not reassemble fragmented traffic, and hence have packet-by-packet basis.  In
   order to enforce their filtering policy based on the information contained in its forwarding policy, the received fragment, as opposed stateless firewall may
   need to the glean information contained in from both the
   reassembled datagram. 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 traffic, many of such firewalls
   typically enforce their policy only on packet, and the entire header chain is contained
   within the first fragment of a
   packet, based on fragment, the assumption that if firewall discards the first fragment is
   dropped, reassembly of the corresponding datagram will fail,
   and thus
   such datagram will be effectively blocked.  However, if allows subsequent fragments to pass.  Because the first fragment fails to include
   was discarded, the entire IPv6 header chain, they might
   have no alternative other than "blindly" allowing or blocking packet cannot be reassembled at the
   corresponding fragment.  If they blindly allow destination.
   Insomuch as the packet, then packet cannot be reassembled, the forwarding policy
   is enforced.

   However, when the firewall can be easily circumvented by intentionally sending is presented with a fragmented packets that fail to include packet and
   the entire IPv6 header chain
   in spans multiple fragments, the first fragment does
   not contain enough information for the firewall to enforce its
   forwarding policy.  Lacking sufficient information, the first stateless
   firewall either forwards or discards that fragment.  On  Regardless of
   the other hand, first-fragments 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 IPv6
   header chain have never been formally
   deprecated and thus, in theory, might be legitimately generated.

6.  Updating RFC 2460

   If an IPv6 packet is fragmented, the first fragment of that IPv6
   packet (i.e., the fragment having a Fragment Offset of 0) MUST
   contain the entire IPv6 header chain. fragment.

   A host that receives an IPv6 a first-fragment that does not contain satisfy the
   entire IPv6 header chain
   above-stated requirements SHOULD drop discard that packet, and also MAY
   send an ICMPv6 error message to the (claimed) source address of the offending
   packet (subject to the sending rules for ICMPv6 errors specified in


   Likewise, an intermediate system (e.g. router, firewall) that
   receives an IPv6 first-fragment that does not contain satisfy the entire IPv6 header chain above-
   stated requirements MAY
   drop discard that packet, and MAY send an ICMPv6
   error message to the
   (claimed) source address of the offending packet (subject
   to the sending 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 drops discards an IPv6 first-fragment because
   it does not contain satisfy the entire IPv6 Header Chain, above-stated requirements, and sends an
   ICMPv6 error message due to that packet drop, the discard, then the ICMPv6 error
   message MUST be Type 4 ("Parameter Problem") and MUST use Code 3 ("First-
   fragment TBD
   ("First-fragment has incomplete IPv6 Header Chain").

   Implementations SHOULD support configuration of whether an ICMPv6
   error/diagnostic message is sent when such packet drops occur.
   Implementations might consider providing not only an enable/disable
   configuration, but also other settings (e.g. rate-limit the sending
   of this kind of ICMPv6 error message).

   Sending this ICMPv6 error message when such packets are dropped can
   be very helpful in diagnosing operational IPv6 network problems, for
   example if recursive tunnels or certain link technologies have
   reduced the end-to-end MTU from larger more common values.  However,
   such ICMPv6 messages also might be operationally problematic, for
   example if an adversary forges the source address on IPv6 first-
   fragment packets that do NOT contain the entire IPv6 Header Chain.
   So configurability about sending these ICMPv6 error messages is very
   important to network operators for this situation.


6.  IANA Considerations

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

       TBD     IPv6 first-fragment has incomplete IPv6 header chain


7.  Security Considerations

   This document describes the interoperability and security
   implications of IPv6 how improperly-fragmented packets or first-fragments that fail to include
   the entire IPv6 header chain.  The security implications include the
   possibility of an attacker evading network security controls such as
   firewalls and Network Intrusion Detection Systems (NIDS) [CPNI-IPv6]. can prevent
   traditional stateless packet filtering.

   This document updates RFC 2460 such that those packets are forbidden,
   thus preventing the aforementioned issues. 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 3) 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].


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, Bill Jouris, Suresh
   Krishnan, Dave Thaler, and Eric Vyncke, for providing valuable
   comments on earlier versions of this document.


9.  References


9.1.  Normative References

   [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.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              December 2005.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [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.


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.

   [RFC6146]  Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
              NAT64: Network Address and Protocol Translation from IPv6
              Clients to IPv4 Servers", RFC 6146, April 2011.

              Gont, F., "Security Assessment of the Internet Protocol
              version 6 (IPv6)",  UK Centre for the Protection of
              National Infrastructure, (available on request).

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