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Versions: (draft-csl-dhc-dhcpv6-unknown-msg-3315update) 00 01 02 03 04 05 06 07 08 RFC 7283

DHC Working Group                                                 Y. Cui
Internet-Draft                                                    Q. Sun
Intended status: Standards Track                     Tsinghua University
Expires: October 26, 2013                                       T. Lemon
                                                           Nominum, Inc.
                                                          April 24, 2013


                    Handling Unknown DHCPv6 Messages
                  draft-ietf-dhc-dhcpv6-unknown-msg-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.  This document updates RFC3315.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 26, 2013.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . . . 3
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Relay Agent Behavior Update . . . . . . . . . . . . . . . . . . 3
     4.1.  Definition of a Valid Message . . . . . . . . . . . . . . . 3
     4.2.  Relaying a Message towards Server . . . . . . . . . . . . . 4
     4.3.  Relaying a Message towards Client . . . . . . . . . . . . . 4
   5.  Client and Server Behavior Update . . . . . . . . . . . . . . . 4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   8.  Contributors List . . . . . . . . . . . . . . . . . . . . . . . 5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5

































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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 [RFC3315] 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.  This document updates [RFC3315].


2.  Requirements Language

   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 [RFC2119].


3.  Problem Statement

   The relay agent is bound to send a message either to the server or to
   the client.  But RFC3315 doesn't specify how the relay agent can find
   out it should send a message towards the server or towards the
   client.

   Another issue is that, there is no statement in RFC3315 about what a
   relay agent should do when receiving message types it doesn't
   recognize.  The relay agent isn't required to relay the messages, nor
   advised to drop them.

   In addition, there is no specific requirement of the client or server
   on dealing with an unknown message in RFC3315.


4.  Relay Agent Behavior Update

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

4.1.  Definition of a Valid Message

   Section 20.1 of [RFC3315] states that:

   "When a relay agent receives a valid message to be relayed, it
   constructs a new Relay-forward message."



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   However it doesn't specify what a valid message is.  In this
   document, we define that a message is valid for constructing a new
   Relay-forward message if it is not a Relay-reply message.

4.2.  Relaying a Message towards Server

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

4.3.  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],
   regardless of the message type in Relay Message Option.


5.  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.


6.  Security Considerations

   As the relay agent will forward all unknown types of DHCPv6 messages,
   a malicious attacker can interfere with the relaying function by
   constructing fake DHCPv6 messages with arbitrary type code.  The same
   problem may happen 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.

   So in most cases, if clients are not upgraded there should be minimal



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   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.

   Nothing in this update should be construed to mean that relay agents
   may not be administratively configurable to drop messages on the
   basis of the message type, for security reasons (e.g., in a
   firewall).  The sole purpose of requiring relay agents to relay
   unknown messages is to ensure that when legitimate new messages are
   defined in the protocol, relay agents, even if they were manufactured
   prior to the definition of these new messages, will, by default,
   succeed in relaying such messages.


7.  IANA Considerations

   This document does not include an IANA request.


8.  Contributors List

   Many thanks for Bernie Volz, Cong Liu and Yuchi Chen's contributions
   to the draft.


9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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



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   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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