Network Working Group R. Droms
Internet-Draft J. Schnizlein
Expires: May 2, 2002 Cisco Systems
Nov 2001
802.1X Credentials Sub-option for the DHCP Relay Agent Information
Option
draft-droms-agentopt-8021x-00.txt
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
The IEEE 802.1X protocol provides authenticated layer 2 network
access. As part of the authentication for 802.1X, a device such as a
switch or a wireless LAN access point can receive credentials from
the authentication authority identifying the user of a device
requesting access. These credentials can then be used by a DHCP
server in the selection of an IP address for assignment to the device
through its DHCP client. The 802.1X Credentials sub-option allows an
access device that implements 802.1X and that can create DHCP Relay
Agent options to pass along credentials for the user of a device
received during 802.1X authentication to a DHCP server.
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1. Introduction and Background
The 802.1X Credentials sub-option for the DHCP Relay Agent option
provides a way through which network elements can pass information
obtained through IEEE 802.1X [2] layer-2 authentication to a DHCP
server. IEEE 802.1X is a mechanism through which a device such as a
switch or a wireless LAN access point can authenticate the identity
of the user of a device before providing layer 2 network access. In
802.1X authenticated access, a device must first exchange some
authentication credentials with the network access device. The
access device then supplies these credentials to an authentication
server, which either confirms or denies the identity of the user of
the device requesting network access. The access device, based on
the reply of the authentication server, then allows or denies network
access to the requesting device.
Figure 1 summarizes the message exchange among the participants in
IEEE 802.1X authentication.
+-----------------+
|Device requesting|
|network access |
+-----------------+
| ^
| |
(1) Request for access
| |
| (4) Access granted
v |
+-----------------+
| Access Device |
|(802.1X and DHCP |
| relay agent} |
+-----------------+
| ^
| |
(2) Request for authentication
| |
| (3) Authentication confirm/deny
v |
+-----------------+
| Authentication |
| Service |
+-----------------+
Figure 1: Message exchange in IEEE 802.1X
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In the application described in this document, the access device acts
as an 802.1X authenticator and adds DHCP relay agent options to DHCP
messages. During 802.1X authentication, the reply message from the
authentication server carries additional identification information
or credentials to the access device. The access device stores these
credentials locally. When the access device subsequently forwards
DHCP messages from the network device, the access device adds the
identification information in an 802.1X Credentials sub-option. The
802.1X Credentials sub-option is another suboption of the Relay Agent
option [5].
2. Terminology
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 [1].
2.1 General Terminology
Authentication server Provides a service that confirms the
identity of a network entity; e.g., a RADIUS [3] server
Authentication credentials Data provided by a device to authenticate
its identity
Identity credentials Data from the authentication server that
can be used to identify an authenticated device
2.2 DHCP Terminology
The following terms are used in conjunction with DHCP [4].
DHCP relay agent Forwards DHCP messages between DHCP
clients and servers
DHCP server Provides configuration parameters to
clients through DHCP messages
DHCP client Requests configuration parameters from
servers through DHCP messages
Relay agent option A DHCP message option used by DHCP relay
agents to pass information to DHCP servers [5]
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2.3 802.1X Terminology
The following terms are used in conjunction with the IEEE 802.1X
protocol.
Authenticator Confirms the identity of the supplicant and
controls the access of the supplicant to the network
Supplicant A device attempting to obtain network service
through the authenticator
3. 802.1X Credentials sub-option format
The 802.1X Credentials Sub-option is a new sub-option for the DHCP
Relay Agent option.
The format of the 802.1X Credentials sub-option is:
SubOpt Len 802.1X Information
code
+-------+-----+------+------+------+------+--...-+------+
| TBD | N | b1 | b2 | b3 | b4 | | bN |
+-------+-----+------+------+------+------+--...-+------+
The 802.1X credentials are carried as opaque data bytes b1...bN.
4. Client Behavior
To enable the use of the 802.1X Credentials sub-option, the host must
use both 802.1X and DHCP. The host need not make any other special
provision for the use of the 802.1X Credentials sub-option.
5. DHCP Relay Agent Behavior
When the DHCP relay agent receives a DHCP message from the client, it
MAY append a DHCP Relay Agent option containing the 802.1X
Credentials sub-option, along with any other relay agent sub-options
it is configured to supply. The 802.1X Credentials sub-option MUST
contain the credentials from the 802.1X authentication service. The
DHCP relay agent MUST NOT add 802.1X Credentials sub-options beyond
one in a message.
The specification of the mechanism through which the authentication
service supplies the credentials to the 802.1X authenticator is
beyond the scope of this document. The 802.1X Credentials sub-option
may be used for any credentials supplied to the authenticator through
whatever protocol used to communicate with the authentication
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service.
6. Server Behavior
When the DHCP server receives a message from an relay agent
containing an 802.1X Credentials sub-option, it extracts the contents
of the of the sub-option and uses that information in selecting
configuration parameters for the client.
7. Security Considerations
DHCP as currently defined provides no authentication or security
mechanisms. Potential exposures to attack are discussed in section 7
of the DHCP protocol specification in RFC 2131.
The DHCP Relay Agent option depends on a trusted relationship between
the DHCP relay agent and the server, as described in section 5 of RFC
3046. Because the 802.1X credentials are not encrypted or protected
against modification in any way, the contents can be spoofed or
modifed by hostile devices in an unsecured network.
8. IANA Considerations
IANA has assigned the value of TBD for the DHCP Relay Agent
Information option sub-option code for this sub-option. This
document does not define any new namespaces or other constants for
which IANA must maintain a registry.
9. Terms of Use
Cisco has a pending patent which relates to the subject matter of
this Internet Draft. If a standard relating to this subject matter
is adopted by IETF and any claims of any issued Cisco patents are
necessary for practicing this standard, any party will be able to
obtain a license from Cisco to use any such patent claims under
openly specified, reasonable, non-discriminatory terms to implement
and fully comply with the standard.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Institute of Electrical and Electronics Engineers, "Port based
Network Access Control", IEEE Standard 802.1X, March 2001.
[3] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865, June
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2000.
[4] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131,
March 1997.
[5] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046,
January 2001.
Authors' Addresses
Ralph Droms
Cisco Systems
250 Apollo Drive
Chelmsford, MA 01824
USA
EMail: rdroms@cisco.com
John Schnizlein
Cisco Systems
9123 Loughran Road
Fort Washington, MD 20744
USA
EMail: jschnizl@cisco.com
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