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Handling Unknown DHCPv6 Messages
draft-ietf-dhc-dhcpv6-unknown-msg-07

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7283.
Authors Yong Cui , Qi Sun , Ted Lemon
Last updated 2014-03-27 (Latest revision 2014-03-26)
Replaces draft-csl-dhc-dhcpv6-unknown-msg-3315update
RFC stream Internet Engineering Task Force (IETF)
Formats
Reviews
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Sheng Jiang
Shepherd write-up Show Last changed 2014-01-07
IESG IESG state Became RFC 7283 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Needs a YES. Needs 10 more YES or NO OBJECTION positions to pass.
Responsible AD Brian Haberman
Send notices to dhc-chairs@tools.ietf.org, draft-ietf-dhc-dhcpv6-unknown-msg@tools.ietf.org, jiangsheng@huawei.com
IANA IANA review state IANA OK - No Actions Needed
draft-ietf-dhc-dhcpv6-unknown-msg-07
DHC Working Group                                                 Y. Cui
Internet-Draft                                                    Q. Sun
Updates: 3315 (if approved)                          Tsinghua University
Intended status: Standards Track                                T. Lemon
Expires: September 27, 2014                                Nominum, Inc.
                                                          March 26, 2014

                    Handling Unknown DHCPv6 Messages
                  draft-ietf-dhc-dhcpv6-unknown-msg-07

Abstract

   DHCPv6 is not specific about handling messages with unknown types.
   This memo describes the problems and defines how a DHCPv6 server,
   client or relay agent should behave when receiving unknown DHCPv6
   messages.  This document also provides advice for authors of future
   documents defining new messages sent from DHCP servers to DHCP relay
   agents, and should be read by potential authors of such documents.
   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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   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 September 27, 2014.

Copyright Notice

   Copyright (c) 2014 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Relay Agent Behavior Update . . . . . . . . . . . . . . . . .   3
     4.1.  A Valid Message for Constructing a New Relay-forward
           Message . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Relaying a Message toward Server  . . . . . . . . . . . .   4
     4.3.  Relaying a Message toward Client  . . . . . . . . . . . .   5
   5.  Client and Server Behavior Update . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Contributors List . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   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 messages with
   unrecognized types.  This document describes the problems and defines
   the behavior of a DHCPv6 server, client or relay agent when handling
   unknown DHCPv6 messages.

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].

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3.  Problem Statement

   When a relay agent receives a message, it decides to send the message
   either toward the server or toward the client.  However, RFC 3315
   does not explicitly describe how the relay agent can determine
   whether it should send a message toward the server or the client,
   although this is implied by the message definitions in RFC3315.

   Another issue is that RFC3315 does not specify what a relay agent
   should do if it does not recognize a received message; the relay
   agent is not required to relay the message, nor advised to drop the
   message.  If relaying an unknown message, the relay agent is given no
   guidance about whether to send it toward the server or the client.

   In addition, there is no specific requirement for dealing with
   unknown messages by the client or server in RFC3315.

   Note it is expected that most future DHCPv6 messages will not be used
   to communicate directly with relay agents (though they may need to be
   relayed by relay agents).

4.  Relay Agent Behavior Update

   Relay agents relay messages toward servers and clients according to
   the message type.  The Relay-reply message is sent toward the client.
   The Relay-forward message and other types of messages are sent toward
   the server.

   We say "toward the client" and "toward the server" because relay
   agents may be chained together, so a relay message may be sent
   through multiple relay agents along the path to its destination.
   Relay-reply messages specify a destination address; the relay agent
   extracts the encapsulated message and sends it to the specified
   destination address.  Any message other than a Relay-reply does not
   have such a specified destination, so it follows the default
   forwarding path configured on the relay agent, which is always toward
   the server.

   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.

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4.1.  A Valid Message for Constructing a New Relay-forward 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."

   It does not define which types of messages are valid for constructing
   Relay-Forward messages.  In this document, we specify the definition
   as follows.

     The message is valid for constructing a new Relay-forward message:

     (a) if the message is a Relay-forward message, or

     (b) if the relay agent receives the message for which it does not
     identify itself as the target.

   New DHCP message types may be defined in future that are sent,
   unsolicited, to relay agents.  Relay agents that do not implement
   these messages will not recognize such messages as being intended for
   them.  A relay agent that implements this specification will
   therefore forward such messages to the DHCP servers to which it is
   configured to relay client messages.

   At this time, no such message types have been specified.  If such a
   message is specified in the future, it is possible that this would
   result in needless load on DHCP servers.  If such a message type is
   defined in a future specification, authors may need to consider some
   strategy for identifying non-conforming relays and not sending such
   messages to them.

   However, since DHCP servers do not respond to unknown messages, this
   is unlikely to create significant load, and therefore is likely to be
   unnecessary.

4.2.  Relaying a Message toward Server

   If the relay agent receives a Relay-forward message, Section 20.1.2
   of [RFC3315] defines the required behavior.  If the relay agent
   receives messages other than Relay-forward and Relay-reply and the
   relay agent does not recognize its message type, it MUST forward them
   as is described in Section 20.1.1 of [RFC3315].

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4.3.  Relaying a Message toward Client

   If the relay agent receives a Relay-reply message, it MUST process
   the message as is defined in Section 20.2 of [RFC3315], regardless of
   the type of the message encapsulated in the Relay Message Option.

5.  Client and Server Behavior Update

   A client or server MUST silently discard any received DHCPv6 message
   with an unknown message type.

6.  Security Considerations

   This document creates no new security issues that are not already
   present in RFC3315.  By explicitly documenting the correct handling
   of unknown messages, this document, if implemented, reduces any
   security exposure that might result from incorrect handling of
   unknown messages.  The following issues are issues that could already
   be present with section 23 of [RFC3315], but we discuss them in
   detail here as guidance for implementors.

   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 constructs the fake DHCP message with a known type code.

   Clients and servers that implement this specification will discard
   unknown DHCPv6 messages.  Since RFC3315 did not specify either relay
   agent, client or server behavior in the presence of unknown messages,
   it is possible that some servers or clients that have 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 agent; 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
   additional risk; at sites where only servers and relay agents 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

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   firewall).

7.  IANA Considerations

   This document does not include an IANA request.

8.  Contributors List

   Many thanks to Bernie Volz, Tomek Mrugalski, Sheng Jiang, Cong Liu
   and Yuchi Chen for their contributions to the document.

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
   Beijing  100084
   P.R.China

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

   Qi Sun
   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: Ted.Lemon@nominum.com

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