Network Working Group                                             Y. Cui
Internet-Draft                                                    Q. Sun
Intended status: Standards Track                     Tsinghua University
Expires: September 27, 2013                                     T. Lemon
                                                           Nominum, Inc.
                                                          March 26, 2013


                    Handling Unknown DHCPv6 Messages
             draft-csl-dhc-dhcpv6-unknown-msg-3315update-00

Abstract

   Dynamic Host Configuration Protocol version 6 (DHCPv6) isn't specific
   about handling messages with unknown types.  This document describes
   the problems and defines how a DHCPv6 function node should behave in
   this case.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on September 27, 2013.

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

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Relay Agent Behavior Update . . . . . . . . . . . . . . . . .   2
     3.1.  Relaying a Message towards Server . . . . . . . . . . . .   3
     3.2.  Relaying a Message towards Client . . . . . . . . . . . .   3
   4.  Client and Server Behavior Update . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   7.  Contributors List . . . . . . . . . . . . . . . . . . . . . .   4
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   Dynamic Host Configuration Protocol version 6 (DHCPv6) [RFC3315]
   provides a framework for conveying IPv6 configuration information to
   hosts on a TCP/IP network.  But RFC 3315 is not specific about how to
   deal with message with unrecognized types.  This document describe
   the problems and defines the behavior of a DHCPv6 function node in
   this case.

2.  Problem Statement

   The relay agent is bound to send a message to either the server or
   the client.  But RFC 3315 doesn't specify how the relay agent can
   find out that it should send a message towards the server or towards
   the client.

   Another issue is that, there is no statement in RFC 3315 about the
   case that what a relay agent should do if it receives message types
   it doesn't recognize.  RFC 3315 doesn't require it to relay the
   messages, nor advise it to drop them.

   In addition, there is no specific requirement of the client or server
   on dealing with an unknown message in RFC 3315.

3.  Relay Agent Behavior Update

   A relay agent is responsible for relaying messages between the client
   and server.  The Relay-reply message is meant for the client
   (downlink), while the Relay-forward message and other types of
   message is meant for the server (uplink).  A relay agent should
   leverage the information to determine whether it should relay the
   message towards the server or the client.



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3.1.  Relaying a Message towards Server

   If the relay agent received a Relay-forward, Section 20.1.2 of
   [RFC3315] defines the related behavior.  If the relay agent received
   messages other than Relay-forward or Relay-reply, it MUST forward
   them as is described in Section 20.1.1 of [RFC3315].

3.2.  Relaying a Message towards Client

   If the relay agent received a Relay-reply message, it MUST unpack the
   message and forward it as is defined in Section 20.2 of [RFC3315].

4.  Client and Server Behavior Update

   There are chances that the client or server would receive DHCPv6
   messages with unknown types.  In this case, the client or server MUST
   discard the unrecognized messages.

5.  Security Considerations

   As the relay agent will forward all unknown types of DHCPv6 messages,
   a malicious attacker can interference with the relaying function by
   inject fake DHCPv6 messages with arbitrary type code.  But this is
   the same problem happens in current DHCPv4 and DHCPv6 practice where
   the attacker has to construct the fake DHCP message with an known
   type code.

   Clients and servers that implement this specification will discard
   unknown DHCPv6 messages.  Since RFC3315 did not specify either relay,
   client or server behavior in the presence of unknown messages, it is
   possible that some server or client that has not been updated to
   conform to this specification might be made vulnerable to client
   attacks through the relay agent.

   For this reason, we recommend that relay agents, clients and servers
   be updated to follow this new specification.  However, in most
   deployment scenarios, it will be much easier to attack clients
   directly than through a relay; furthermore, attacks using unknown
   message types are already possible on the local wire, yet no known
   vulnerabilities exist.

   So in most cases, if clients are not upgraded there should be minimal
   additional risk; at sites where only servers and relays can be
   upgraded, the incremental benefit of doing so most likely exceeds any
   risk due to vulnerable clients.

6.  IANA Considerations




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   This document does not include an IANA request.

7.  Contributors List

   Many thanks for Cong Liu and Yuchi Chen's contribution to the draft.

8.  Normative References

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

Authors' Addresses

   Yong Cui
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6260-3059
   Email: yong@csnet1.cs.tsinghua.edu.cn


   Qi Sun
   Tsinghua University
   Department of Computer Science, Tsinghua University
   Beijing  100084
   P.R.China

   Phone: +86-10-6278-5822
   Email: sunqi@csnet1.cs.tsinghua.edu.cn


   Ted Lemon
   Nominum, Inc.
   2000 Seaport Blvd
   Redwood City, CA  94063
   USA

   Phone: +1-650-381-6000
   Email: mellon@nominum.com








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