Internet DRAFT - draft-csl-dhc-dhcpv6-unknown-msg-3315update
draft-csl-dhc-dhcpv6-unknown-msg-3315update
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
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This Internet-Draft will expire on September 27, 2013.
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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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