Network Working Group                                           J. Abley
Request for Comments: 5095                                       Afilias
Updates: 2460, 4294                                            P. Savola
Category: Standards Track                                      CSC/FUNET
                                                         G. Neville-Neil
                                                 Neville-Neil Consulting
                                                           December 2007

             Deprecation of Type 0 Routing Headers in IPv6

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.


   The functionality provided by IPv6's Type 0 Routing Header can be
   exploited in order to achieve traffic amplification over a remote
   path for the purposes of generating denial-of-service traffic.  This
   document updates the IPv6 specification to deprecate the use of IPv6
   Type 0 Routing Headers, in light of this security concern.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Deprecation of RH0  . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Operations  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     4.1.  Ingress Filtering . . . . . . . . . . . . . . . . . . . . . 3
     4.2.  Firewall Policy . . . . . . . . . . . . . . . . . . . . . . 3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 4
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 5

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1.  Introduction

   [RFC2460] defines an IPv6 extension header called "Routing Header",
   identified by a Next Header value of 43 in the immediately preceding
   header.  A particular Routing Header subtype denoted as "Type 0" is
   also defined.  Type 0 Routing Headers are referred to as "RH0" in
   this document.

   A single RH0 may contain multiple intermediate node addresses, and
   the same address may be included more than once in the same RH0.
   This allows a packet to be constructed such that it will oscillate
   between two RH0-processing hosts or routers many times.  This allows
   a stream of packets from an attacker to be amplified along the path
   between two remote routers, which could be used to cause congestion
   along arbitrary remote paths and hence act as a denial-of-service
   mechanism.  An 88-fold amplification has been demonstrated using this
   technique [CanSecWest07].

   This attack is particularly serious in that it affects the entire
   path between the two exploited nodes, not only the nodes themselves
   or their local networks.  Analogous functionality may be found in the
   IPv4 source route option, but the opportunities for abuse are greater
   with RH0 due to the ability to specify many more intermediate node
   addresses in each packet.

   The severity of this threat is considered to be sufficient to warrant
   deprecation of RH0 entirely.  A side effect is that this also
   eliminates benign RH0 use-cases; however, such applications may be
   facilitated by future Routing Header specifications.

   Potential problems with RH0 were identified in 2001 [Security].  In
   2002 a proposal was made to restrict Routing Header processing in
   hosts [Hosts].  These efforts resulted in the modification of the
   Mobile IPv6 specification to use the type 2 Routing Header instead of
   RH0 [RFC3775].  Vishwas Manral identified various risks associated
   with RH0 in 2006 including the amplification attack; several of these
   vulnerabilities (together with other issues) were later documented in

   A treatment of the operational security implications of RH0 was
   presented by Philippe Biondi and Arnaud Ebalard at the CanSecWest
   conference in Vancouver, 2007 [CanSecWest07].  This presentation
   resulted in widespread publicity for the risks associated with RH0.

   This document updates [RFC2460] and [RFC4294].

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2.  Definitions

   RH0 in this document denotes the IPv6 Extension Header type 43
   ("Routing Header") variant 0 ("Type 0 Routing Header"), as defined in

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

3.  Deprecation of RH0

   An IPv6 node that receives a packet with a destination address
   assigned to it and that contains an RH0 extension header MUST NOT
   execute the algorithm specified in the latter part of Section 4.4 of
   [RFC2460] for RH0.  Instead, such packets MUST be processed according
   to the behaviour specified in Section 4.4 of [RFC2460] for a datagram
   that includes an unrecognised Routing Type value, namely:

      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 Parameter Problem, Code 0, message to the packet's
      Source Address, pointing to the unrecognized Routing Type.

   IPv6 implementations are no longer required to implement RH0 in any

4.  Operations

4.1.  Ingress Filtering

   It is to be expected that it will take some time before all IPv6
   nodes are updated to remove support for RH0.  Some of the uses of RH0
   described in [CanSecWest07] can be mitigated using ingress filtering,
   as recommended in [RFC2827] and [RFC3704].

   A site security policy intended to protect against attacks using RH0
   SHOULD include the implementation of ingress filtering at the site

4.2.  Firewall Policy

   Blocking all IPv6 packets that carry Routing Headers (rather than
   specifically blocking Type 0 and permitting other types) has very
   serious implications for the future development of IPv6.  If even a

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RFC 5095                   Deprecation of RH0              December 2007

   small percentage of deployed firewalls block other types of Routing
   Headers by default, it will become impossible in practice to extend
   IPv6 Routing Headers.  For example, Mobile IPv6 [RFC3775] relies upon
   a Type 2 Routing Header; wide-scale, indiscriminate blocking of
   Routing Headers will make Mobile IPv6 undeployable.

   Firewall policy intended to protect against packets containing RH0
   MUST NOT simply filter all traffic with a Routing Header; it must be
   possible to disable forwarding of Type 0 traffic without blocking
   other types of Routing Headers.  In addition, the default
   configuration MUST permit forwarding of traffic using a Routing
   Header other than 0.

5.  Security Considerations

   The purpose of this document is to deprecate a feature of IPv6 that
   has been shown to have undesirable security implications.  Specific
   examples of vulnerabilities that are facilitated by the availability
   of RH0 can be found in [CanSecWest07].  In particular, RH0 provides a
   mechanism for traffic amplification, which might be used as a denial-
   of-service attack.  A description of this functionality can be found
   in Section 1.

6.  IANA Considerations

   The IANA registry "Internet Protocol Version 6 (IPv6) Parameters"
   should be updated to reflect that variant 0 of IPv6 header-type 43
   ("Routing Header") is deprecated.

7.  Acknowledgements

   This document benefits from the contributions of many IPV6 and V6OPS
   working group participants, including Jari Arkko, Arnaud Ebalard, Tim
   Enos, Brian Haberman, Jun-ichiro itojun Hagino, Bob Hinden, Thomas
   Narten, Jinmei Tatuya, David Malone, Jeroen Massar, Dave Thaler, and
   Guillaume Valadon.

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8.  References

8.1.  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.

   [RFC4294]       Loughney, J., "IPv6 Node Requirements", RFC 4294,
                   April 2006.

8.2.  Informative References

   [CanSecWest07]  Biondi, P. and A. Ebalard, "IPv6 Routing Header
                   Security", CanSecWest Security Conference 2007,
                   April 2007.

   [Hosts]         Savola, P., "Note about Routing Header Processing on
                   IPv6 Hosts", Work in Progress, February 2002.

   [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.

   [RFC3775]       Johnson, D., Perkins, C., and J. Arkko, "Mobility
                   Support in IPv6", RFC 3775, June 2004.

   [RFC4942]       Davies, E., Krishnan, S., and P. Savola, "IPv6
                   Transition/Co-existence Security Considerations",
                   RFC 4942, September 2007.

   [Security]      Savola, P., "Security of IPv6 Routing Header and Home
                   Address Options", Work in Progress, March 2002.

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Authors' Addresses

   Joe Abley
   Afilias Canada Corp.
   Suite 204, 4141 Yonge Street
   Toronto, ON  M2P 2A8

   Phone: +1 416 673 4176
   EMail: jabley@ca.afilias.info

   Pekka Savola

   EMail: psavola@funet.fi

   George Neville-Neil
   Neville-Neil Consulting
   2261 Market St. #239
   San Francisco, CA  94114

   EMail: gnn@neville-neil.com

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