Internet DRAFT - draft-ietf-dhc-v6-relay-radius
draft-ietf-dhc-v6-relay-radius
DHC Working Group Wing Cheong Lau
Internet Draft The Chinese University
Document: draft-ietf-dhc-v6-relay-radius-02.txt of Hong Kong
Expires: August 2, 2006 Feb 03, 2006
DHCPv6 Relay agent RADIUS Attribute Option
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79 [1].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html"
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 RADIUS
Attributes Option (RRAO) which extends the set of DHCPv6 options as
defined in RFC 3315 and 3376. Following its DHCPv4 counterpart, the
new option is inserted by the DHCPv6 relay agent when forwarding
client-originated DHCPv6 packets to a DHCPv6 server. Servers
recognizing the RRAO 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.
Expires Aug 2006 [Page 1]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
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. Introduction...................................................2
2. Terminology....................................................5
2.1 DHCP Terminology...........................................5
2.2 RADIUS Terminology.........................................6
3. Relay agent RADIUS Attributes Option for DHCPv6................6
3.1 Relay Agent Operation......................................7
3.2 Server Operation...........................................8
3.3 DHCP Client Behavior.......................................9
4. Security Considerations........................................9
5. IANA Considerations...........................................10
6. Acknowledgments...............................................10
7. Intellectual Property Statement...............................10
8. Full copyright statement......................................11
Author's Address.................................................11
References.......................................................11
1. Introduction
In some access network environment, a Network Access Server (NAS)
enabling authenticated network access may also act as a DHCPv6 relay
agent to forward requests and responses between the access client and
a DHCPv6 server within the network. The DHCPv6 server may be used for
assigning various configuration parameters for the client[9,10]. The
NAS, 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
device requesting access. The Relay agent RADIUS Attributes Option
(RRAO) enables the NAS, which doubles as a DHCPv6 relay agent, to
Expires - Aug 2006 [Page 2]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
pass along attributes for the user of a device received during RADIUS
authentication to a DHCP server [3].
The IEEE 802.1X [9] access authentication mechanism is an example
through which a 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 IEEE 802.1X authenticated
access, an access client must first exchange some authentication
credentials with the NAS. The NAS 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 NAS, 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 such access authentication environment.
+------------------+
| Device |
| requesting |
| network access |
+------------------+
| ^
| |
(1) Request for access
| |
| (4) Success/Failure
v |
+-------------------+
| NAS |
| which also acts |
| as a |
|DHCPv6 relay agent)|
+-------------------+
| ^
| |
(2) Request for authentication
| |
| (3) Access-Accept/Reject
v |
+-----------------+
| RADIUS |
| Server |
+-----------------+
Figure 1
In the application described in this document, the NAS also acts as a
DHCPv6 relay agent. It adds a DHCPv6 Relay agent RADIUS Attributes
Expires - Aug 2006 [Page 3]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
option (RRAO) 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 DHCPv6 RRAO.
The 3GPP2 access authentication mechanism is another 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 [10]. 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 2 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 |
|server/relay agent)|
+-------------------+
| ^
| |
(2) Request for authentication
| |
| (3) Access-Accept/Reject
v |
+-----------------+
| RADIUS |
| Server |
+-----------------+
Figure 2
Expires - Aug 2006 [Page 4]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
Without the DHCPv6 RRAO described in this document, the NAS and the
DHCPv6 server would need to co-locate within the PDSN (which is the
case in [10]) in order to allow the DHCPv6 server to make use of the
information carried by the RADIUS Access-Accept message while
generating DHCPv6 replies. However, forcing the DHCPv6 server to co-
locate with the PDSN is undesirable as it imposes unnecessary
constraints on network topology and configuration. Furthermore, since
[10] already requires the PDSN to behave as a DHCPv6 relay-agent for
some types of queries, e.g. for dynamic configuration of the DNS
server or SIP proxy for the MS, requiring the PDSN to be double as a
DHCPv6 server will cause unnecessary implementation and processing
complexity.
By using the RRAO described in this document, the PDSN no longer
needs to take the dual role with respect to DHCPv6. It only needs to
be DHCPv6 Relay Agent (and a NAS). 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 IEEE 802.1X and 3GPP2 access authentication as two
examples to motivate the use of the RRAO by a NAS. The RRAO described
in this document is not limited to use in conjunction with IEEE
802.1X or 3GPP2. It can be used to carry RADIUS attributes obtained
by the relay agent for any reason but is constrained by RADIUS
semantics.
The scope of applicability of this specification is such that the NAS
(which acts as a DHCPv6 relay agent), any other participating DHCPv6
relay agent, the DHCPv6 server and DHCPv6 client should be within the
same administrative domain while the RADIUS service involved may span
multiple administrative domains. See the Section 4 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
Expires - Aug 2006 [Page 5]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
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 RADIUS Attributes Option for DHCPv6
To support the capability of the NAS/ DHCP relay agent as described
in Section 1, we introduce the DHCPv6 equivalent of the DHCPv4 Relay
Agent Information Option and the 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 RADIUS
Attribute Option (RRAO) 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 and [13], the new option is
inserted by the DHCP relay agent when forwarding client-originated
DHCP packets to a DHCP server. Servers recognizing the RRAO 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 format of the RRAO 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_RRAO | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RADIUS Attributes |
| (variable no. of octets) |
. .
Expires - Aug 2006 [Page 6]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
option-code OPTION_RRAO (TBD). This is the DHCP option
code for the Relay agent RADIUS Attribute Option
option-len An unsigned integer giving the length of the
RADIUS Attributes field in octets.
RADIUS Attributes
This consists of a sequence of RADIUS Attributes
encoded according to the encoding rules in
RFC 2865.
3.1 Relay Agent Operation
The adding of the DHCP RRAO SHOULD be configurable, and SHOULD be
disabled by default.
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 RRAO,
along with other option(s), e.g. the Interface-Id 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].
The RRAO MUST only contain the attributes provided in the RADIUS
Access/Accept message. The DHCP relay agent MUST NOT add more than
one RRAO in a message.
The relay agent MUST include the User-Name and IPv6 Framed-Pool
attributes in the RRAO 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 in an instance of the RRAO. The following table lists
attributes that MAY be included:
# Attribute
Expires - Aug 2006 [Page 7]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
--- ---------
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])
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 RRAO, along with other option(s), as described in
Section 3.1.1, 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 RRAO 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.
3.2 Server Operation
DHCP servers unaware of the RRAO 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 RRAO 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 RRAO 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 RRAO to perform such checking.
When the DHCP server receives a message from a relay agent containing
a RRAO, it extracts the contents of the option and MAY use that
information as a hint in selecting configuration parameters for the
client. If the relay agent forwards RADIUS attributes not included in
the table in Section 3.1.1, the DHCP server SHOULD ignore them. If
Expires - Aug 2006 [Page 8]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
the DHCP server uses attributes not specified in the table, it might
result in side effects not anticipated in the existing RADIUS
specifications.
DHCP servers claiming to support the RRAO MUST echo the entire
contents of the RRAO in all of its relay-replies. The nesting of the
echoed RRAO(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].
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. Security Considerations
The DHCP RRAO 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 RRAO may be prevented by a perimeter defense that blocks
these options unless the relay agent is trusted, a deeper defense
using IPsec [5] SHOULD be deployed as well. Refer to Section 21.1 of
RFC 3315 [3] for detail IPsec configurations required to protect
communications between the DHCP relay agent(s) and server.
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 RRAO may also convey information that
identifies a specific host or a specific user on the network. In
practice, this information is not exposed outside the internal
service-provider network, where DHCP messages are usually confined.
Administrators who configure data that is going to be used in the
RRAO 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 RRAO 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
Expires - Aug 2006 [Page 9]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
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 an
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.
5. IANA Considerations
IANA is requested to assign a new option code, in the registry of
DHCP option codes, for the DHCP Relay agent RADIUS Attributes Option.
6. Acknowledgments
Many thanks to R. Droms, M. Patrick, 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 author would
also like to thank R. Droms, B. Volz, T. Lemon, K. Chowdhury, P.
Barany, T. Hardie, R. Hsu, M. Lioy, A.C. Mahendran, R. Rezaiifar, S.
Veerepalli and J. Wang for their helpful discussions.
7. 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
rights which may cover technology that may be required to practice
Expires - Aug 2006 [Page 10]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
this document. Please address the information to the IETF Executive
Director.
8. Full copyright statement
Copyright (C) The Internet Society (2006).
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.
Author's Address
Wing Cheong Lau
Department of Information Engineering
The Chinese University of Hong Kong
Shatin, N.T.
Hong Kong
Email: wclau@ie.cuhk.edu.hk , lau@ieee.org
References
Normative References
[1]Bradner, S., "Intellectual Property Rights in IETF Technology",
BCP 79, RFC 3979, March 2005.
[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.
[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.
Expires - Aug 2006 [Page 11]
DHCPv6 Relay agent RADIUS Attributes Option Feb 2006
[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]Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port based Network Access Control",
IEEE Standard 802.1X, March 2001.
[10]3GPP2 X.S0011-002-D v.0.4, "cdma2000 Wireless IP Network
Standard:Simple IP and Mobile IP services," Work in progress.
[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.
Expires - Aug 2006 [Page 12]
