IPv6 Reverse Path Forwarding ICMP error message
draft-hain-ipv6-rpf-icmp-00

Abstract

This document specifies an icmp error message for use when the IPv6 source address has failed a reverse-path-forwarding (RPF) check.

The draft is being discussed on the ipv6@ietf.org list.

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Table of Contents

1.  Introduction
2.  Terminology
3.  Mechanisms
    3.1.  Overview
    3.2.  ReversePathForwarding ICMP Error Message
4.  IANA Considerations
5.  Security Considerations
6.  Acknowledgements
7.  Pending comments
8.  References
    8.1.  Normative References
    8.2.  Informative References
§  Author's Address

1.  Introduction

A form of ingress traffic filtering commonly known as reverse path forwarding check is discussed in RFC 2827 [RFC2827] (Abley, J., “Deprecation of Type 0 Routing Headers in IPv6,” December 2007.)While the specific discussion in that document is focused on protecting against source address spoofing attacks by silently dropping the packets, there are instances when multi-homed IPv6 nodes have a mismatch between the source address and the selected path where the desired action SHOULD be to inform and provide a hint. This document defines an icmp error message to inform a source that the packet is being dropped because the source address used would not work as a destination for packets returning over this path. To avoid the situation where this informational back channel could be used as a denial of service attack, these icmp error messages MUST be rate limited.

2.  Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.) [RFC2119].

3.  Mechanisms

3.1.  Overview

3.2.  ReversePathForwarding ICMP Error Message

Informing the origin that the source prefix is not appropriate for the next hop as a symmetric return path.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         Prefix Length                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                 Source Prefix for this Path                   |
   +                                                               +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     MAC-type      |              MAC-length                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                 Message Authentication Code                   |
   +                                                               +
   |                                                               |
   +                                                               +

IPv6 Fields:

   Destination Address

                        Copied from the Source Address field of the
                        invoking packet.

   ICMPv6 Fields:

   Type           ???? --- 6

   Code           0 - unsigned
		    1 - signed

   Reserved             32-bit reserved field.  Initialized to zero
                        for transmission; ignored on reception.


   MAC-type       0 - unused
		    1 - HMAC-SHA1
		    2 - AES-CMAC
		    ...

   MAC-length    Length of the message authentication option

   MAC           Value of the message authenticator

The optional authentication covers the source and destination address of this specific packet exchange, plus the return-via address.

4.  IANA Considerations

This specification registers an IPv6 ICMP error message type

5.  Security Considerations

The IPv6 ICMP RPF-error messages represents a potential denial of service attack vector, and therefore these messages MUST be rate limited by receivers.

6.  Acknowledgements

The general need for some way to inform multi-homed IPv6 nodes about an RPF check failure has been discussed in multiple sessions at IETF 77 and 78.

7.  Pending comments

8.  References

8.1. Normative References

8.2. Informative References

Author's Address