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802.1X fundamentals
802.1X is a port-based network access control protocol initially proposed by the IEEE 802 LAN/WAN
committee for securing wireless LANs (WLANs), and it has also been widely used on Ethernet networks for
access control.
802.1X controls network access by authenticating the devices connected to 802.1X-enabled LAN ports.
Architecture of 802.1X
802.1X operates in the client/server model. It comprises three entities: the client (the supplicant), the
network access device (the authenticator), and the authentication server, as shown in a.
a. Architecture of 802.1X
The client is a user terminal seeking access to the LAN. It must have 802.1X software to authenticate
to the network access device.
The network access device authenticates the client to control access to the LAN. In a typical 802.1X
environment, the network access device uses an authentication server to perform authentication.
The authentication server is the entity that provides authentication services for the network access
device. It authenticates 802.1X clients by using the data sent from the network access device, and
returns the authentication results for the network access device to make access decisions. The
authentication server is typically a Remote Authentication Dial-in User Service (RADIUS) server. In a
small LAN, you can also use the network access device as the authentication server.
Controlled/uncontrolled port and port authorization
status
802.1X defines two logical ports for the network access port: controlled port and uncontrolled port. Any
packet arriving at the network access port is visible to both logical ports.
The controlled port allows incoming and outgoing traffic to pass through when it is in the authorized
state, and denies incoming and outgoing traffic when it is in the unauthorized state, as shown in a. The
controlled port is set in the authorized state if the client has passed authentication, and in the
unauthorized state, if the client has failed authentication.
The uncontrolled port is always open to receive and transmit EAPOL frames.
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