dhc T. Lemon
Internet-Draft Nominum
Intended status: Standards Track Q. Wu
Expires: April 14, 2011 Huawei
October 11, 2010
Relay-Supplied DHCP Options
draft-ietf-dhc-dhcpv6-relay-supplied-options-03
Abstract
This document describes a mechanism whereby a DHCPv6 relay agent can
provide options to a DHCPv6 server that the DHCPv6 server can then
provide to the DHCPv6 client in certain restricted cases where this
is necessary.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 14, 2011.
Copyright Notice
Copyright (c) 2010 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Summary . . . . . . . . . . . . . . . . . . . . . . . 3
3. Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. RSOO-enabled options . . . . . . . . . . . . . . . . . . . . . 4
5. DHCP Relay Agent Behavior . . . . . . . . . . . . . . . . . . . 5
6. DHCP Server Behavior . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
The DHCPv6 specification [RFC3315] allows DHCP relay agents to
forward DHCPv6 messages between clients and servers that are not on
the same IPv6 link. In some cases the DHCP relay agent has
information not available to the DHCP server that would be useful to
provide to a DHCP client. For example, the DHCP client may need to
learn the EAP local domain name [I.D-ietf-hokey-ldn-discovery] for
use in EAP re-authentication [RFC5296], which is known to the relay
agent but not the server.
The DHCPv6 protocol specification does not provide a mechanism
whereby the relay agent can provide options to the client. This
document extends DHCP with a mechanism that allows DHCP relay agents
to propose options for the server to send to DHCP clients.
This document is not intended to provide a general mechanism for
storing client configuration information in the relay agent. Rather,
it is intended to address specific use cases where only the relay
agent has information needed by the client. This extension is not
applicable to DHCP options in general, but rather provided as a
mechanism for new specifications that require this functionality.
1.1. 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].
1.2. Terminology
The following terms and acronyms are used in this document:
DHCP Dynamic Host Configuration Protocol Version 6 [RFC3315]
RSOO Relay-Supplied Options option
2. Protocol Summary
DHCP clients do not support a mechanism for receiving options from
relay agents--the function of the relay agent is simply to deliver
the payload from the server. Consequently, in order for the DHCP
relay agent to provide options to the client, it sends those options
to the DHCP server, encapsulated in a Relay-Supplied Options option.
The DHCP server can then choose to place those options in the
response it sends to the client.
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3. Encoding
In order to supply options for the DHCP server to send to the client,
the relay agent sends a Relay-Supplied Options option in the Relay-
Forward message. This option encapsulates whatever options the relay
agent wishes to provide to the DHCPv6 server.
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_RSOO | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| suboptions...
+-+-+-+-+-+-+-+-+-+-+-+
OPTION_RSOO Relay-Supplied Options code (TBD).
option-length Length of Relay-Supplied Options option.
suboptions One or more DHCPv6 options.
4. RSOO-enabled options
Unless specifically called out as an RSOO-enabled option, no DHCP
option should appear in an RSOO. Specifications that describe RSOO-
enabled options MUST reference this specification, and MUST state
that the option they define is RSOO-enabled. No DHCP option
specified prior to the issuance of this specification is RSOO-
enabled.
A current list of RSOO-enabled options can be found in the list
titled "Options Permitted in the Relay-Supplied Options option"
maintained at http://www.iana.org/assignments/dhcpv6-parameters.
DHCP option specifications that define RSOO-enabled options MUST add
text similar to the following to their IANA considerations section;
"random relay option" should be replaced with the name of the option
being defined in the specification:
We request that IANA add the name "random relay option" to the
registry titled "Options Permitted in the Relay-Supplied Options
Option" maintained at
http://www.iana.org/assignments/dhcpv6-parameters.
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5. DHCP Relay Agent Behavior
DHCP relay agents that implement this specification MUST be
configurable not to send the Relay-Supplied Options option.
Relay agents MAY include a Relay-Supplied Options option in the
option payload of a Relay-Forward message. Relay agents MUST NOT
modify the contents of any message before forwarding it to the DHCP
client.
Relay agents MUST NOT send non-RSOO-enabled options in the Relay-
Supplied Options option.
Relay agents implementing this specification SHOULD have a
configuration parameter that determines whether or not they will
relay a Relay-Forward message toward the DHCP server if it contains a
Relay-Supplied Options option.
Relay agents that have this configuration parameter and that are
configured to enable this behavior MUST silently discard any Relay-
Forward packet that contains a Relay-Supplied Options option.
Implementations that can be configured in this way MUST examine all
Relay-Forward encapsulations, not just the outer encapsulation.
6. DHCP Server Behavior
DHCP servers that implement this specification MUST examine each
option contained in an RSOO to see if it is an RSOO-enabled option.
DHCP servers MUST silently discard any option contained in an RSOO
that is not RSOO-enabled. DHCP server implementations SHOULD have a
user-configurable list of RSOO-enabled options, so that new RSOO-
enabled options do not require software to be updated.
DHCP servers normally construct a list of options that are candidates
to send to the DHCP client, and then construct the DHCP packet
according to section 17.2.2 of DHCPv6 [RFC3315].
If the server implementing this specificaton receives an RSOO, it
SHOULD add any options that appear in the RSOO for which it has no
internal candidate to the list of options that are candidates to send
to the DHCP client. The server SHOULD discard any options that
appear in the RSOO for which it already has one or more candidates.
Aside from the addition of options from the RSOO, the DHCP server
should then construct a DHCP packet as it normally would, and
transmit it to the DHCP client as described in DHCPv6 [RFC3315].
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DHCP servers may receive multiply-nested Relay-Forward messages
containing conflicting values for options contained in Relay Supplied
Options options in these messages.
When such a conflict exists, the DHCP server MUST choose no more than
one of these options to forward to the client. The DHCP server MUST
not forward more than one of these options to the client.
By default, the DHCP server MUST choose the innermost value--the
value supplied by the relay agent closest to the DHCP client, to
forward to the DHCP client.
DHCP server implementations MAY provide other heuristics for choosing
which one of a set of such conflicting options to forward to the
client, as long as the specified behavior is the default behavior.
7. Security Considerations
This document provides a mechanism whereby a relay agent can inject
options into the response the DHCP server sends to the DHCP client.
In general it is expected that RSOO-enabled options will be specified
because they only make sense when originating from the relay agent.
This is true of existing use cases.
In the event that some new RSOO-enabled option is specified that can
originate from either the server or the relay agent, this should be
addressed in the security considerations section of the document that
specifies the use of that option.
In some environments, there is an interface on one side of which is
the client, and zero or more routers, and on the other side of which
is a network managed by a monolithic or effectively monolithic
administrative entity. Nodes and routers on the client side of the
interface are not controlled by this entity, and are considered
"untrusted." Nodes and routers on the other side of this interface
are considered trusted.
It is possible for a relay agent on the untrusted side of this
interface to supply a Relay-Supplied Options option containing one or
more RSOO-enabled options that would override the same option or
options that were provided by a relay agent on the trusted side of
the interface.
In environments where this is a possibility, network administrators
are advised to use relay agents that are capable of dropping Relay-
Forward messages containing the Relay-Supplied Options option, and
are advised to configure those relays to drop such messages.
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Note, however, that this will only be effective if the message from
the DHCP server to the DHCP client is authenticated as specified in
Section 21 of DHCP Version 6 [RFC3315], or using some similar
mechanism. Without this authentication, the relay agent on the
untrusted portion of the network can simply modify the DHCP server's
response in transit back to the DHCP client, and there is no way for
the client to detect that this has happened.
8. IANA Considerations
We request that IANA assign one new option code from the registry of
DHCP Option Codes maintained at
http://www.iana.org/assignments/dhcpv6-parameters. This option code
will be assigned to the Relay-Supplied Options option.
We request that the IANA create a new registry on the same
assignments page, titled "Options Permitted in the Relay-Supplied
Options Option". This option will contain a list of names of options
from the DHCP Option Codes list. Currently, the list is empty.
9. References
9.1. 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.
9.2. Informative References
[I.D-ietf-hokey-ldn-discovery]
Zorn, G., Wu, Q., and Y. Wang, "The Local Domain Name
DHCPv6 Option", draft-ietf-hokey-ldn-discovery-05 (work in
progress), September 2010.
[RFC5296] Narayanan, V. and L. Dondeti, "EAP Extensions for EAP Re-
authentication Protocol (ERP)", RFC 5296, August 2008.
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Authors' Addresses
Ted Lemon
Nominum
2000 Seaport Blvd
Redwood City, CA 94063
USA
Phone: +1 650 381 6000
Email: mellon@nominum.com
Qin Wu
Huawei Technologies Co., Ltd.
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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