DHC Working Group Ralph Droms
Cisco Systems
Internet Draft Wing Cheong Lau
Document: draft-droms-dhc-v6-relayopt-00.txt Qualcomm
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DHCPv6 Relay Agent Information Option
Status of this Memo
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Abstract
This document introduces the capabilities of the DHCPv4 Relay Agent
Information Option in RFC 3046 and the corresponding RADIUS-
Attributes Sub-option to DHCPv6. In particular, the document
describes a new DHCPv6 option called the Relay Agent Information
option which extends the set of DHCPv6 options as defined in RFC 3315
and 3376. Following its DHCPv4 counterpart as defined in RFC 3046,
the new option is inserted by the DHCPv6 relay agent when forwarding
client-originated DHCPv6 packets to a DHCPv6 server. Servers
recognizing the Relay Agent Information option may use the
information to implement IP address or other parameter assignment
policies. The DHCP Server echoes the option back verbatim to the
relay agent in server-to-client replies, and the relay agent strips
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the option before forwarding the reply to the client. The Relay Agent
Information option is organized as a single DHCPv6 option that
contains one or more "sub-options" that convey information known by
the relay agent. A RADIUS Attributes Sub-option, following its
DHCPv4 counterpart, is also defined.
Conventions used in this document
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 [2].
The use of the standard keywords MUST, SHOULD, MUST NOT and SHOULD
NOT within this specification are with respect to RADIUS clients and
servers that implement the optional features of this specification,
do not create any normative requirements outside of that scope and do
not modify the base RADIUS specifications, such as RFC2865 [6] or
RFC2866 [11].
Throughout this document, "DHCP" refers to DHCP for IPv6 unless
explicitly stated otherwise.
Table of Contents
1. Motivation and Introduction....................................2
2. Terminology....................................................4
2.1 DHCP Terminology...........................................4
2.2 RADIUS Terminology.........................................5
3. Relay Agent Information Option for DHCPv6......................5
3.1 Relay Agent Operation......................................7
3.2 Server Operation...........................................8
3.3 DHCP Client Behavior.......................................8
4. Relay Agent Information Sub-options............................8
4.1 RADIUS Attributes sub-option...............................8
5. Security Considerations.......................................10
6. IANA Considerations...........................................11
7. Acknowledgments...............................................11
8. Intellectual Property Statement...............................11
9. Full copyright statement......................................12
Authors' Addresses...............................................12
References.......................................................12
1. Motivation and Introduction
In 3GPP2 networks, the Packet Data Service Node (PDSN) provides the
function of a Network Access Server (NAS) to enable authenticated
network access of its clients, i.e. the mobile stations (MS). The
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PDSN also acts as a DHCPv6 relay agent to forward requests and
responses between an MS and a DHCPv6 server within the network. The
DHCPv6 server may be used for assigning DNS server, Mobile IPv6 Home
agent (HA), Mobile IPv6 Home address (HoA) [9,10] and other
configuration parameters for the MS. The PDSN, using RADIUS as an
authentication authority, will receive attributes from a RADIUS
server that may be used by the DHCP server in the selection of
configuration parameters to be delivered to the MS through its DHCP
client. The Relay Agent Information option, together with the RADIUS
Attributes sub-option enable a network element like the PDSN in 3GPP2,
to pass along attributes for the user of a device received during
RADIUS authentication to a DHCP server.
The RADIUS Attributes sub-option for the DHCP Relay Agent Information
option provides a way in which a NAS, such as the 3GPP2 PDSN, can
pass attributes obtained from a RADIUS server to a DHCP server [3].
The 3GPP2 access authentication mechanism is an example through which
a PDSN (which doubles as the NAS) can authenticate the identity of
the user of a device before providing network access using RADIUS as
the Authentication Service specified in [6]. In 3GPP2 authenticated
access, an MS must first exchange some authentication credentials
with the PDSN. The PDSN then supplies these credentials to a RADIUS
server, which eventually sends either an Access-Accept or an Access-
Reject in response to an Access-Request. The PDSN, based on the reply
of the RADIUS server, then allows or denies network access to the
requesting device.
Figure 1 summarizes the message exchange among the participants in
3GPP2 network access authentication.
+------------------+
|Mobile Station(MS)|
| requesting |
| network access |
+------------------+
| ^
| |
(1) Request for access
| |
| (4) Success/Failure
v |
+-------------------+
| 3GPP2 PDSN |
| (Acts as NAS |
| and |
|DHCPv6 relay agent)|
+-------------------+
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| ^
| |
(2) Request for authentication
| |
| (3) Access-Accept/Reject
v |
+-----------------+
| RADIUS |
| Server |
+-----------------+
Figure 1
In the application described in this document, the PDSN acts as a NAS
as well as a DHCPv6 relay agent. It adds a DHCP Relay Agent
Information option which includes a RADIUS Attributes sub-option to
DHCP messages. At the successful conclusion of network access
authentication, a RADIUS Access-Accept provides attributes for
service authorizations to the NAS. The NAS stores these attributes
locally. When the NAS subsequently forwards DHCP messages from the
device requesting network access, the NAS adds these attributes in a
RADIUS Attributes Sub-option for the Relay Agent Information option.
This document uses 3GPP2 access authentication as an example to
motivate the use of the Relay Agent Information option and the RADIUS
Attributes sub-option by a NAS. The Relay Agent Information option is
not limited to use in conjunction with RADIUS sub-option when other
sub-options are defined in the future. The RADIUS Attributes sub-
option for the Relay Agent Information option described in this
document is not limited to use in conjunction with 3GPP2 and can be
used to carry RADIUS attributes obtained by the relay agent for any
reason. That is, the sub-option is not limited to use with 3GPP2,
but is constrained by RADIUS semantics.
The scope of applicability of this specification is such that the NAS
(which acts as a DHCP relay agent), any other participating DHCP
relay agent, the DHCP server and DHCP client should be within the
same administrative domain while the RADIUS service involved may span
multiple administrative domains. See the Section 5 for details of
security considerations when this specification is deployed with
RADIUS service operating across multiple administrative domains.
Global interoperability of this specification, across arbitrary
administrative domains, is not supported.
2. Terminology
2.1 DHCP Terminology
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The following terms are used as defined in RFC3315 and RFC3736: DHCP
relay agent, DHCP server, DHCP client, Stateless DHCP.
2.2 RADIUS Terminology
The following terms are used in conjunction with RADIUS:
RADIUS server: A RADIUS server is responsible for receiving user
connection requests, authenticating the user, and then returning
all configuration information necessary for the client to deliver
service to the user.
Attribute: A Type-Length-Value tuple encapsulating data elements as
defined in RFC 2865 [6].
NAS: A Network Access Server (NAS) provides access to the network and
operates as a client of RADIUS. The client is responsible for passing
user information to designated RADIUS servers, and then acting on the
response which is returned.
3. Relay Agent Information Option for DHCPv6
To support the capability of a PDSN as described in Section 1, we
introduce the DHCPv6 counterpart of the DHCPv4 Relay Agent
Information Option and the related RADIUS Attributes Sub-option as
defined in RFC3046 [12] and [13] respectively. In particular, this
document describes a new DHCPv6 option called the Relay Agent
Information option which extends the set of DHCPv6 options as defined
in RFC 3315 [3] and 3736 [4]. Following its DHCPv4 counterpart as
defined in RFC 3046, the new option is inserted by the DHCPv6 relay
agent when forwarding client-originated DHCPv6 packets to a DHCPv6
server. Servers recognizing the Relay Agent Information option may
use the information to implement IP address or other parameter
assignment policies. The DHCP Server echoes the option back verbatim
to the relay agent in server-to-client replies, and the relay agent
strips the option before forwarding the reply to the client.
The new DHCPv6 Option is called the Relay Agent Information Option.
It is a "container" option for specific agent supplied sub-options.
The format of the Relay Agent Information option follows that of the
DHCP Options as defined in Section 22.1 of RFC 3315 [3] as follows:
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_RELAY_INFO | option-len |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Agent Information Field |
| (variable no. of octets) |
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_RELAY_INFO (TBD). This is the DHCP option
code for the Relay Agent Information Option
option-len An unsigned integer giving the length of the
Agent Information Field in octets.
Agent Information Field
This consists of a sequence of
SubOpt/Length/Value tuples for each sub-option,
encoded in the following manner:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|sub-option-code|sub-option-len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .
. sub-option-value field .
. (variable no. of octets) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
sub-option-code An unsigned integer identifying the specific
sub-option type carried in this sub-option.
sub-option-len An unsigned integer giving the length the
sub-option value in octets.
sub-option-value field
This consists of a sequence of octets carrying
the sub-option value.
Since at least one sub-option must be defined, the minimum option-len
for the Relay Agent Information option length is two (2). The length
an sub-option shall be the number of octets in that sub-option's
value field. A sub-option length may be zero. The sub-options need
not appear in sub-option code order.
The initial assignment of DHCP Relay Agent Sub-options is as follows:
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DHCP Agent Sub-Option Description
Sub-option Code
--------------- ----------------------
SUBOPT_RADIUS (TBD) RADIUS-Attributes Sub-option
3.1 Relay Agent Operation
Overall adding of the DHCP relay agent option SHOULD be configurable,
and SHOULD be disabled by default. Relay agents SHOULD have separate
configurables for each sub-option to control whether it is added to
client-to-server packets.
The operation of relay agents for specific sub-options is specified
with that sub-option.
Relay agents are NOT required to monitor or modify client-originated
DHCP packets addressed to a server unicast address.
3.1.1 Relaying a Message from a Client
When a relay agent receives a valid DHCP message to be relayed from a
client, it constructs a new Relay-forward message per Section 20.1.1
of RFC 3315 [3] and then adds to the Relay-forward message the Relay
Agent Information Option if it is configured to do so. The relay
agent must be aware of the recommendations on packet sizes and the
use of fragmentation in Section 5 of RFC 2460 [8].
3.1.2 Relaying a Message from a Relay Agent
When a relay agent receives a valid Relay-forward message from
another relay agent closer to the client, regardless of whether the
message already includes a Relay Agent Information option or not, the
relay agent shall construct a new Relay-forward message per Section
20.1.2 of RFC 3315 [3] and then add to this newly created Relay-
forward message the Relay Agent Information Option if it is
configured to do so. The relay agent must be aware of the
recommendations on packet sizes and the use of fragmentation in
Section 5 of RFC 2460 [8].
3.1.3 Relaying a Replay-reply Message
The Relay Agent Information option echoed by a server MUST be removed
by the relay agent which added it when forwarding a server-to-client
response back to the client.
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3.2 Server Operation
DHCP servers unaware of the Relay Agent Information option will
ignore the option upon receive and will not echo it back on
responses. This is the specified server behavior for unknown
options.
DHCP servers claiming to support the Relay Agent Information option
MUST discard the message and increment an error count if a Relay
Agent Information option was added by a DHCP client but not by a
relay agent. (This situation can be identified by the nesting of a
Relay Agent Information option inside the content of the Relay
Message option created by the first-hop relay agent.) We put the
responsibility of such checking to the DHCP server instead of the
relay agents in order to simplify the operations of the latter.
Furthermore, it is unreasonable to require a relay agent not
supporting/ understanding the Relay Agent Information option to
perform such checking.
DHCP servers claiming to support the Relay Agent Information option
MUST echo the entire contents of the Relay Agent Information option
in all of its relay-replies. The nesting of the echoed Relay-Agent
Information option(s) within the possibly nested relay-reply message
MUST be according to the nesting order of those options within the
original the Relay-forward message. DHCP servers must be aware of the
recommendations on packet sizes and the use of fragmentation in
Section 5 of RFC 2460 [8].
The operation of DHCP servers for specific sub-options is specified
with that sub-option.
3.3 DHCP Client Behavior
Relay agent options are exchanged only between relay agents and DHCP
server, so DHCP clients are never aware of their use.
4. Relay Agent Information Sub-options
4.1 RADIUS Attributes sub-option
The RADIUS Attributes Sub-option is a sub-option for the DHCP
Relay Agent option.
The format of the RADIUS Attributes sub-option is:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SUBOPT_RADIUS |sub-option-len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .
. RADIUS attributes .
. (variable no. of octets) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The RADIUS attributes are encoded as a sequence of octets according
to the encoding rules in RFC 2865 [6].
4.1.1 DHCP Relay Agent Behavior for the RADIUS Attributes Sub-option
When the DHCP relay agent receives a DHCP message from the client, it
MAY append a DHCP Relay Agent Information option containing the
RADIUS Attributes sub-option, along with any other sub-options it is
configured to supply. The RADIUS Attributes sub-option MUST only
contain the attributes provided in the RADIUS Access/Accept message.
The DHCP relay agent MUST NOT add more than one RADIUS Attributes
sub-option in a message.
The relay agent MUST include the User-Name and IPv6 Framed-Pool
attributes in the RADIUS Attributes sub-option if available, and MAY
include other attributes.
In order to avoid dependencies between the address allocation and
other state information between the RADIUS server and the DHCP server,
the DHCP relay agent SHOULD include only the attributes in the table
below an instance of the RADIUS Attributes sub-option. The table
lists attributes that MAY be included:
# Attribute
--- ---------
1 User-Name (RFC 2865 [6])
6 Service-Type (RFC 2865)
26 Vendor-Specific (RFC 2865)
27 Session-Timeout (RFC 2865)
100 Framed-IPv6-Pool (RFC 3162 [7])
4.1.2 DHCP Server Behavior
When the DHCP server receives a message from a relay agent containing
a RADIUS Attributes sub-option, it extracts the contents of the sub-
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option and uses that information in selecting configuration
parameters for the client. If the relay agent forwards RADIUS
attributes not included in the table in Section 4.1.1, the DHCP
server SHOULD ignore them. If the DHCP server uses attributes not
specified here, it might result in side effects not anticipated in
the existing RADIUS specifications.
5. Security Considerations
The DHCP Relay Agent Information option depends on a trusted
relationship between the DHCP relay agent and the server. If a client
message is relayed through multiple relay agents, each of the relay
agents must have established independent, pairwise trust
relationships. While the introduction of fraudulent relay-agent
options can be prevented by a perimeter defense that blocks these
options unless the relay agent is trusted, a deeper defense using,
e.g. IPsec [5] as described in Section 21.1 of RFC 3315 [3] SHOULD be
deployed as well.
There are several data in a DHCP message that convey information that
may identify an individual host on the network. Depending on the type
of data included, the Relay Agent Information option and its sub-
options may also convey information that identifies a specific host
or a specific user on the network. In practice, this information
isn't exposed outside the internal service-provider network, where
DHCP messages are usually confined. Administrators who configure data
that's going to be used the Relay Agent Information option and its
sub-options should be careful to use data that are appropriate for
the types of networks they administer. If DHCP messages travel
outside the service-provider's own network, or if the sub-option
values may become visible to other users, that may raise privacy
concerns for the access provider or service provider.
The RADIUS protocol [6] was designed for intra-domain use, where the
NAS, proxy, and home server exist within a single administrative
domain, and proxies may be considered a trusted component. However,
under roaming situation, the NAS, proxies, and home server will
typically be managed by different administrative entities. As a
result, inter-domain RADIUS operations are inherently required for
roaming applications, and proxies cannot necessarily be trusted.
Refer to Section 7 of RFC 2609 for a detailed security threat
analysis, limitations and precautions of operating RADIUS in a inter-
domain environment. In general, robust and secure operations of
RADIUS across multiple administrative domains require pre-established
agreement, mutual trust, and secure communications channel amongst
all the participating domains.
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6. IANA Considerations
IANA is requested to assign a new option code, in the registry of DHCP
option codes, for the DHCP Relay Agent Information Option.
IANA is also requested to maintain a new number space of "DHCPv6
Relay Agent Information Option Sub-options". The initial sub-options
are described in Section 4 of this document. In particular, IANA is
requested to assign Sub-option number for RADIUS-Attributes Sub-
option.
IANA assigns future DHCP Relay Agent Information Option Sub-options
with a "IETF Consensus" policy as described in RFC 2434. Future
proposed sub-options are to be referenced symbolically in the
Internet-Drafts that describe them, and shall be assigned numeric
codes by IANA when approved for publication as an RFC.
7. Acknowledgments
Many thanks to M. Patrick, R. Droms, J. Schnizlein, M. Stapp, R.
Johnson and T. Palaniappan as this document is based on their work on
the DHCPv4 relay agent information option RFC3046 [12] and the
related sub-options [13,14]. The document follows closely the
original structure and borrows text from [12,13,14]. The 2nd author
would also like to thank P. Barany, T. Hardie, R. Hsu, M. Lioy, A.C.
Mahendran, R. Rezaiifar, S. Veerepalli and J. Wang for their helpful
discussions.
8. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
claims of rights made available for publication and any assurances of
licenses to be made available, or the result of an attempt made to
obtain a general license or permission for the use of such
proprietary rights by implementors or users of this specification can
be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
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rights which may cover technology that may be required to practice
this document. Please address the information to the IETF Executive
Director.
9. Full copyright statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78 and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Authors' Addresses
Ralph Droms
Cisco Systems
1414 Massachusetts Avenue
Boxborough, MA 01719
U.S.A.
Email: rdroms@cisco.com
Wing Cheong Lau
Qualcomm
5775 Morehouse Drive
San Diego, CA 92121
U.S.A.
Phone: 858-651-5032
Email: lau@qualcomm.com
References
Normative References
[1]Bradner, S., "Intellectual Property Rights in IETF Technology",
BCP 79, RFC 3668, Feb. 2004.
[2]Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3]Droms, R., Ed., "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
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[4]Droms, R., "Stateless Dynamic Host Configuration Protocol (DHCP)
Service for IPv6", RFC 3736, April 2004.
[5]Kent, S. and Atkinson R., "Security Architecture for the Internet
Protocol", RFC 2401, Nov. 1998.
[6]Rigney, C., Willens, S., Rubens, A. and Simpson, W., "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865, June
2000.
[7]Aboba, B., Zorn, G. and Mitton, D., "RADIUS and IPv6", RFC 3162,
Aug. 2001.
[8]Deering, S and Hinden, R., "Internet Protocol Version 6 (IPv6)
Specification", RFC 2460, Dec. 1998.
Informative References
[9]3GPP2 X.S0011-002-D v.0.4, "cdma2000 Wireless IP Network
Standard:Simple IP and Mobile IP services," Work in progress.
[10]Johnson, D, Perkins, C. and Arkko, J., "Mobility Support in
IPv6", RFC 3775, June 2004.
[11]Rigney, C. "RADIUS Accounting", RFC 2866, June 2000.
[12]M.Patrick, "DHCP Relay Agent Information Option", RFC3046, Jan
2001.
[13]Droms, R., Schnizlein J., "RADIUS Attributes Sub-option for the
DHCP Relay Agent Information Option", draft-ietf-dhc-agentopt-
radius-08.txt, August 18, 2004.
[14]Stapp, M., Johnson, R., and Palaniappan, T., "Vendor-Specific
Information Sub-option for the DHCP Relay Agent Option", draft-
ietf-dhc-vendor-suboption-00.txt, Work-in-progress, Aug. 2004.
[15]Aboba B. and Vollbrecht J., "Proxy Chaining and Policy
Implementation in Roaming", RFC 2607, June 1999.
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