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Versions: 00                                                            
Internet Engineering Task Force                                P. Savola
Internet Draft                                                 CSC/FUNET
Expiration Date: August 2002
                                                           February 2002

           Note about Routing Header Processing on IPv6 Hosts


Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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   [IPV6] specifies routing header processing for nodes.  The text is
   sufficiently ambiguous where the behaviour of hosts is concerned, and
   can be perceived as a security threat.  This draft clarifies the
   issue by referring to IPv4 Host Requirements document and requiring
   hosts must not, by default, forward routing headers outside of the

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Internet Draft      draft-savola-ipv6-rh-hosts-00.txt      February 2002

1. Issue with Routing Header Processing

   [IPV6] specifies routing header processing for nodes.  The text is
   sufficiently ambiguous, especially the 3rd paragraph on page 13, to
   make one believe that routing header forwarding should be enabled on
   all nodes (including hosts); a few implementations are known to have
   interpreted the specification this way.

   For clarification, it should be noted that IPv4 Host Requirements
   [HOSTREQ], especially section 3.3.5 should be interpreted to apply
   here where appropriate; the interpretation of [IPV6] is that every
   node must be able to process routing headers, but not every node
   needs to have that processing enabled.

   See Appendix A for an example set of IPv6 requirements for routing
   header forwarding.

2. Security Considerations

   This draft and [RHHASEC] discuss security considerations of
   processing packets with a routing header.

   [HOSTREQ] permits implementations to perform "local source-routing",
   that is, forwarding routing header out on the same interface it was
   received from, without restrictions even on hosts.  This is a
   security threat, as pointed out in [RHHASEC], and it is recommended
   that IPv6 implementations will not do that.

   Moreover, as [RHHASEC] points out, forwarding routing headers inside
   the same node has residual security threats as well: consider a host
   with two interfaces that belong to different security zones.  These
   kind of nodes are often "security gateways", though, and some may see
   this as an acceptable risk.

3. Acknowledgements

   Francis Dupont for long and colourful discussion on the RFC2460
   interpretation, Vlad Yasevich for pointing out an RFC2460 forwarding
   definition and Erik Nordmark for refining the rules.  The issue was
   raised primarily due to Mobile IPv6 concerns.

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Internet Draft      draft-savola-ipv6-rh-hosts-00.txt      February 2002

4. References

   [IPV6]      Deering, S., Hinden, R., "Internet Protocol, Version 6
               (IPv6) Specification", RFC 2460, December 1998.

   [HOSTREQ]   Braden, R. (Editor) "Requirements for Internet Hosts
               -- Communication Layers", RFC1122, October 1989.

   [RHHASEC]   Savola, P. "Security of IPv6 Routing Header and
               Home Address Options", work-in-progress,
               draft-savola-ipv6-rh-ha-security-01.txt, November 2001.

Author's Address

   Pekka Savola
   Espoo, Finland
   EMail: psavola@funet.fi

A. An example set of rules for IPv6 RH forwarding for hosts

   Here, abbreviation 'RH packet' is used to mean a packet with routing
   header which has segments left > 0 and would be processed at the node
   (that is, destination address is an address of the node).

   A host MUST NOT by default forward RH packets out of the node.  This
   option MAY be configurable, but MUST default to disabled.

   A host MAY restrict forwarding RH packets in the node as well, e.g.
   by disabling all routing header processing by default.  [Note: the
   author believes this should be a SHOULD]

   A host MAY provide some mechanisms of allowing acceptable routing
   header use, for example, allow RH where the address-to-be-changed and
   source address are the same, or allow forwarding out of the same
   interface the packet was received from.

   A host which forwards source routed packets MUST behave the same way
   as a router doing this e.g. in terms of sending ICMP error messages.

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