Client-Inserted Client Link-Layer Address Options in DHCPv6
draft-templin-client-cllao-00.txt

Abstract

RFC6939 presents a method for DHCPv6 relay agents to insert a Client Link Layer Address Option (CLLAO) in a DHCPv6 Relay-Forward message. In some cases, however, the DHCPv6 client may need to insert a CLLAO in its message on its own behalf even though it is on the same link as the DHCPv6 server. This document discusses client-inserted CLLAOs.

Status of This Memo

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Table of Contents

• 1. Introduction
• 2. Client-Inserted CLLAOs
• 3. IANA Considerations
• 4. Security Considerations
• 5. Acknowledgements
• 6. References
• 6.1. Normative References
• 6.2. Informative References
• Author's Address

1. Introduction

[RFC6939] specifies a method for DHCPv6 relays[RFC3315] to insert a Client Link-Layer Address Option (CLLAO) in Relay-Forward messages. This provides a means for a first-hop relay to inform the DHCPv6 server of the link-layer address of the DHCPv6 client on the client<->relay link. However, on some links it may be necessary for the server to receive a CLLAO even when it is on the same link as the client. In that case, the client itself must insert the CLLAO.

Asymmetric Extended Route Optimization (AERO) [I-D.templin-aerolink] is an example of a link where it may be difficult or impossible for the DHCPv6 server to determine the DHCPv6 client's link-layer address through normal socket API operations. In that case, if the client inserts a CLLAO option the server can discover the client's link-layer address by examining the option fields of the DHCPv6 message instead of the message headers. The following section specifies the protocol for client-inserted CLLAOs.

2. Client-Inserted CLLAOs

When a DHCPv6 client is on the same link as the server, and the server requires a means for discovering the client's link-layer address, the client inserts a CLLAO option [RFC6939] in its DHCPv6 messages and writes the link-layer address of the sending interface in the "link-layer address" field.

When a DHCPv6 server is on the same link as the client, and the client includes a CLLAO option in its DHCPv6 messages, the server processes the CLLAO option locally as necessary and returns the CLLAO option in its DHCPv6 replies.

When a DHCPv6 relay on the same link as a client forwards the client's DHCPv6 messages, and the server requires a means for discovering the client's link-layer address, the relay follows the specifications in [RFC6939].

A DHCPv6 client MUST NOT include a CLLAO option if it is not on the same link as the server.

3. IANA Considerations

This document introduces no IANA considerations.

4. Security Considerations

When DHCPv6 authentication [RFC3315] and/or DHCPv6 Security [I-D.ietf-dhc-sedhcpv6] are used, the DHCPv6 client/server MUST NOT include the CLLAO option in security signature calculations. This means that the link-layer address in the CLLAO could be rewritten by a link-layer switching element on the path from the client to the server and not detected by the security mechanism. However, such a condition would only be possible on unsecured links where link-layer switching elements present a man-in-the-middle attack threat.

5. Acknowledgements

6. References

6.1. Normative References

6.2. Informative References

Author's Address