Handling Unknown DHCPv6 Messages
The information below is for an old version of the document.
This is an older version of an Internet-Draft that was ultimately published as RFC 7283.
|Authors||Yong Cui , Qi Sun , Ted Lemon|
|RFC stream||Internet Engineering Task Force (IETF)|
GENART Telechat review (of -06) by Suresh Krishnan Almost ready
GENART Last Call review (of -05) by Suresh Krishnan Almost ready
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||I-D Exists|
|Send notices to||(None)|
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 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 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 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 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 Cui, et al. Expires October 26, 2013 [Page 1] Internet-Draft Handling Unknown DHCPv6 Messages April 2013 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 Cui, et al. Expires October 26, 2013 [Page 2] Internet-Draft Handling Unknown DHCPv6 Messages April 2013 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." Cui, et al. Expires October 26, 2013 [Page 3] Internet-Draft Handling Unknown DHCPv6 Messages April 2013 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 Cui, et al. Expires October 26, 2013 [Page 4] Internet-Draft Handling Unknown DHCPv6 Messages April 2013 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: firstname.lastname@example.org Qi Sun Cui, et al. Expires October 26, 2013 [Page 5] Internet-Draft Handling Unknown DHCPv6 Messages April 2013 Tsinghua University Department of Computer Science, Tsinghua University Beijing 100084 P.R.China Phone: +86-10-6278-5822 Email: email@example.com Ted Lemon Nominum, Inc. 2000 Seaport Blvd Redwood City, CA 94063 USA Phone: +1-650-381-6000 Email: firstname.lastname@example.org Cui, et al. Expires October 26, 2013 [Page 6]