wdiff rfc6939.original rfc6939.txt

Network Working Group
Internet Engineering Task Force (IETF) G. Halwasia
Internet-Draft
Request for Comments: 6939 S. Bhandari
Intended status:
Category: Standards Track W. Dec
Expires: September 12, 2013
ISSN: 2070-1721 Cisco Systems
March 11,
May 2013

Client Link-layer Link-Layer Address Option in DHCPv6
draft-ietf-dhc-dhcpv6-client-link-layer-addr-opt-05

Abstract

This document specifies the format and mechanism that is to be used
for encoding the client link-layer address in DHCPv6 Relay-Forward
messages by defining a new DHCPv6 Client Link-layer Link-Layer Address option.

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 RFC 2119 [RFC2119].

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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
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This Internet-Draft will expire on September 12, 2013.
http://www.rfc-editor.org/info/rfc6939.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 ....................................................2
2. Requirements Language ...........................................2
3. Problem Background and Scenario . . . . . . . . . . . . . . . 2
3. .................................2
4. DHCPv6 Client Link-layer Link-Layer Address Option . . . . . . . . . . . 3
4. .........................4
5. DHCPv6 Relay Agent Behavior . . . . . . . . . . . . . . . . . 4
5. .....................................4
6. DHCPv6 Server Behavior . . . . . . . . . . . . . . . . . . . 4
6. ..........................................4
7. DHCPv6 Client Behavior . . . . . . . . . . . . . . . . . . . 5
7. ..........................................5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. .............................................5
9. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 .........................................5
10. Acknowledgements ...............................................6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. .....................................................6
11.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. ......................................6
11.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 ....................................6

1. Introduction

This specification defines an optional mechanism and the related
DHCPv6 option to allow first-hop DHCPv6 relay agents (relay agents
that are connected to the same link as the client) to provide the
client's link-layer address in the DHCPv6 messages being sent towards
the server.

2. Requirements Language

3. Problem Background and Scenario

The DHCPv4 protocol specification [RFC2131] provides a way to specify the
client link-layer address in the DHCPv4 message header. A DHCPv4
message header has 'htype' and 'chaddr' fields to specify the client
link-layer address type and the link-layer address address, respectively.
The client link-layer address thus learnt learned can be used by the DHCPv4
server and the relay agent in different ways. In some of the deployments
deployments, DHCPv4 servers use 'chaddr' as a customer identifier and
a key for lookup in the client lease database.

With the incremental deployment of IPv6 to existing IPv4 networks,
which results in a dual-stack network environment, there will be
devices that act as both DHCPv4 and DHCPv6 clients. In service
provider deployments, a typical DHCPv4 implementation will use the
client link-layer address as one of the keys to build the DHCP client
lease database. In dual stack scenarios dual-stack scenarios, operators need to be able
to associate DHCPv4 and DHCPv6 messages with the same client
interface, based on an identifier that is common to the interface.
The client link-layer address is such an identifier.

Currently, the DHCPv6 protocol specification [RFC3315] does not define a way
to communicate the client link-layer address to the DHCP server in
cases where the DHCP server is not connected to the same network link
as the DHCP client. The DHCPv6 protocol specification mandates that all
clients to prepare and send DUID a DHCP Unique Identifier (DUID) as the
client identifier option in all the DHCPv6 message exchange. However exchanges.
However, none of these methods provide a simple way to extract a
client's link-layer address. This presents a problem to an operator
who is using an existing DHCPv4 system with the client link-layer
address as the customer identifier, identifier and who desires to correlate
DHCPv6 assignments using the same identifier. [RFC4361] describes a
mechanism for using the same DUID in both DHCPv4 and DHCPv6.
Unfortunately, this specification requires modification of existing
DHCPv4 clients, and has not seen broad adoption in the industry
(indeed, we are not aware of any commercial implementations).

Providing an option in DHCPv6 Relay-Forward messages to carry the
client link-layer address explicitly will help the above mentioned
scenarios. For example, it can be used along with other identifiers
to associate DHCPv4 and DHCPv6 messages from a dual stack dual-stack client.
Further, having the client link-layer address in DHCPv6 will help in proving by
providing additional information in for event debugging and logging
related to the client at the relay agent and the server. The
proposed option may be used in a wide range of
networks, networks; two notable
deployment models are service provider and enterprise network
environments.

4. DHCPv6 Client Link-layer Link-Layer Address Option

The format of the DHCPv6 Client Link-layer Link-Layer Address option is shown
below.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENT_LINKLAYER_ADDR | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| link-layer type (16 bits) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| link-layer address (variable length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

option-code: OPTION_CLIENT_LINKLAYER_ADDR (TBD) (79)
option-length: 2 + length of link-layer address
link-layer type: Client Link-layer link-layer address type. The link-layer
type MUST be a valid hardware type assigned
by the IANA, as described in [RFC0826]
link-layer address: Client Link-layer address.

4. link-layer address

5. DHCPv6 Relay Agent Behavior

DHCPv6 Relay relay agents which that receive messages originating from clients
(for example example, Solicit and Request, but not, for example,
Relay-Forward or Advertise) MAY include the link-layer source address
of the received DHCPv6 message in the Client Link-layer Link-Layer Address option
option, in relayed DHCPv6 Relay-Forward messages. The DHCPv6 Relay relay
agent behavior can depend on configuration that decides whether the
Client
Link-layer Link-Layer Address option needs to be included.

6. DHCPv6 Server Behavior

If the DHCPv6 Server server is configured to store or use a client link-layer link-
layer address, it SHOULD look for the client link-layer address Client Link-Layer Address
option in the Relay-Forward DHCP message of the DHCPv6 Relay relay agent
closest to the client. The mechanism described in this document is
not necessary in the case where the DHCPv6 Server server is connected to the
same network link as the client, because the server can obtain the
link-layer address from the link-layer header of the DHCPv6 message.
If the DHCP server receives a Client Link-layer Link-Layer Address option
anywhere in any encapsulated message that is not a Relay-Forward DHCP
message, the server MUST silently ignore that option.

There is no requirement that a server return this option and its data
in a downstream DHCP message.

7. DHCPv6 Client Behavior

The Client Link-layer Link-Layer Address option is only exchanged between the
relay agents and the servers. DHCPv6 clients are not aware of the
usage of the Client Link-layer Link-Layer Address option. The DHCPv6 client
MUST NOT send the Client
Link-layer Link-Layer Address option, and MUST ignore
the Client Link-layer Link-Layer Address option if received.

8. IANA Considerations

IANA is requested to assign has assigned an option code (79) to OPTION_CLIENT_LINKLAYER_ADDR
from the "DHCP Option Codes" registry
(http://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-
parameters.xml).

8.
(http://www.iana.org/assignments/dhcpv6-parameters/).

9. Security Considerations

It is possible for a rogue DHCPv6 relay agent to insert an incorrect
Client Link Layer Link-Layer Address option for malicious purposes. A DHCPv6
client can also pose as a rogue DHCP relay agent, agent by sending a Relay-
Forward
Relay-Forward message containing an incorrect Client Link Layer Link-Layer
Address option. In either case, it would be possible for a DHCPv6
client to masquerade as the same device as a DHCPv4 client, when in
fact the two are distinct.

One possible attack that could be accomplished using this masquerade
would be in the case where a DHCPv4 client is using DHCPv4 to do a
Dynamic DNS update to install an A record so that it can be reached
by other nodes [RFC4702]. A masquerading DHCPv6 client could use
DHCPv6 to install an a AAAA record with the same name [RFC4704]. Dual-
stack nodes attempting to connect to the DHCPv4 client might then be
tricked into connecting to the masquerading DHCPv6 client instead.

It is possible that there are other attacks that could be
accomplished using this masquerading technique, although the authors
are not aware of any. To prevent masquerades of this sort, DHCP
server administrators are strongly advised to configure DHCP servers
that use this option to communicate with their relay agents using
IPsec
IPsec, as described in Section 21.1 of [RFC3315].

In some networks, it may be the case that the operator of the
physical network and the provider of connectivity over that network
are administratively separate, such that the client link-layer
address Client Link-Layer
Address option would reveal information to one or the other party
that they do not need and could not otherwise obtain. It is also
possible
possible, in some cases cases, that a relay agent might communicate with a
DHCP server over an open network where eavesdropping would be
possible. In these cases, it is strongly recommended, in order to
protect end-user privacy, that network operators use IPsec to provide
confidentiality for messages between the relay agent and the DHCP
server.

10. Acknowledgements

Many thanks to Ted Lemon, Bernie Volz, Hemant Singh, Simon Hobson,
Tina TSOU, Andre Kostur, Chuck Anderson, Steinar Haug, Niall
O'Reilly, Jarrod Johnson, Tomek Mrugalski Mrugalski, and Vincent Zimmer for
their input and review.

10.

11. References

10.1.

11.1. Normative References

[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.

[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.

[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.

10.2.

11.2. Informative References

[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.

[RFC4702] Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host
Configuration Protocol (DHCP) Client Fully Qualified
Domain Name (FQDN) Option", RFC 4702, October 2006.

[RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for
IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN)
Option", RFC 4704, October 2006.

Authors' Addresses

Gaurav Halwasia
Cisco Systems
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India

Phone: +91 80 4429 2703
Email:
EMail: ghalwasi@cisco.com

Shwetha Bhandari
Cisco Systems
Cessna Business Park, Sarjapura Marathalli Outer Ring Road
Bangalore, KARNATAKA 560 087
India

Phone: +91 80 4429 2627
Email:
EMail: shwethab@cisco.com

Wojciech Dec
Cisco Systems
Haarlerbergweg 13-19
1101 CH Amsterdam, Amsterdam 560 087
The Netherlands

Email:

EMail: wdec@cisco.com