IEEE 802.1X
IEEE 802.1X is the standard protocol for allowing hosts and users to be authenticated to the network before
obtaining a connection (port-based network admission control). As well as providing very effective access
control to wireless and other networks, it is being used increasingly for other aspects of host security and
management. (Note that IEEE 802.1X is dependent on the Extensible Authentication Protocol (EAP) , which
is covered by a companion factsheet.)
The Basics
IEEE 802.1X provides the following core capabilities:
• port authorisation on a per-user or per-host basis (the authenticator will not forward frames
until the RADIUS server signals that the supplicant is authorised)
• support for multiple authentication methods (thanks to the use of EAP)
• separation of the authenticator from the back-end authentication server, allowing user
management and policy decision making to be centralised.
An overview of IEEE 802.1X [1] is shown in Figure 1 below. An EAP [2]
exchange encapsulated
directly within Ethernet frames is performed between the supplicant and a RADIUS/EAP Server
(henceforth RADIUS server), via the authenticator. The EAP exchange between the authenticator
and the RADIUS Server is transported by the RADIUS [3] protocol. The RADIUS Server attempts
to validate the supplicant’s credentials against a user database server, and signals the result to the
authenticator. If the result is a success, the authenticator permits forwarding of frames to and from
the supplicant.
Figure
1: IEEE 802.1X overview
Dynamic VLAN Assignment
Besides authentication, perhaps the most useful feature of IEEE 802.1X is dynamic VLAN
assignment [4]. A supplicant authenticates to the RADIUS Server, which returns a RADIUS Access-
Accept packet to the authenticator. The packet also includes attributes indicating which VLAN to
assign to the supplicant’s port. For example, a student logging into a terminal could be assigned
the ‘student VLAN’; a member of staff logging in to the same terminal could be assigned the ‘staff
VLAN’. If no one is logged in, the terminal may have ‘computer’ credentials that permit access to
a ‘maintenance VLAN’ for software updates and remote administration. Note that dynamic VLAN
assignment is not part of the IEEE 802.1X specification, but most vendors have implemented it.
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FACTSHEET
Supplicant
Authenticator
EAP exchange
EAP over LAN
EAP over RADIUS
RADIUS/EAP
server
Access-Accept or Access-Deny
User database
server
Request for password
Password
e.g. LDAP
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