3Com SuperStack 4 Configuration Manual page 248

260 C 11: 802.1
HAPTER X
802.1x Authentication
Process
C
ONFIGURATION
The LAN access control device needs to provide the Authenticator System of
802.1x. The devices at the user side such as the computers need to be installed
with the 802.1x client Supplicant (User) software, for example, the 802.1x client
provided by 3Com (or by Microsoft Windows XP). The 802.1x Authentication
Server system normally stays in the carrier's AAA center.
Authenticator and Authentication Server exchange information through EAP
(Extensible Authentication Protocol) frames. The user and the Authenticator
exchange information through the EAPoL (Extensible Authentication Protocol over
LANs) frame defined by IEEE 802.1x. Authentication data are encapsulated in the
EAP frame, which is to be encapsulated in the packets of other AAA upper layer
protocols (for example, RADIUS) so as to go through the complicated network to
reach the Authentication Server. Such procedure is called EAP Relay.
There are two types of ports for the Authenticator. One is the Uncontrolled Port,
and the other is the Controlled Port. The Uncontrolled Port is always in
bi-directional connection state. The user can access and share the network
resources any time through the ports. The Controlled Port will be in connecting
state only after the user passes the authentication. Then the user is allowed to
access the network resources.
Figure 66 802.1x System Architecture
Supplicant
System
(User)
Supplicant
Controlled
Port
EAPoL
802.1x configures EAP frame to carry the authentication information. The
Standard defines the following types of EAP frames:
EAP-Packet: Authentication information frame, used to carry the
■
authentication information.
EAPoL-Start: Authentication originating frame, actively originated by the user.
■
EAPoL-Logoff: Logoff request frame, actively terminating the authenticated
■
state.
EAPoL-Key: Key information frame, supporting to encrypt the EAP packets.
■
EAPoL-Encapsulated-ASF-Alert: Supports the Alerting message of Alert
■
Standard Forum (ASF).
Authenticator System
Services
offered
by
Authenticators
System
Port
unauthorized
Authenticator
PAE
EAP protocol
exchanges
carried in
Uncontrolled
higher layer
Port protocol
LAN
Authenticator
Server
System
Authenticator
Server