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xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
241
Understanding 802.1x Port-based and MAC-based Network Access
Control
The original intent behind the development of 802.1X was to leverage the characteristics of point-to-point in LANs. As any single
LAN segment in such infrastructures has no more than two devices attached to it, one of which is a Bridge Port. The Bridge Port
detects events that indicate the attachment of an active device at the remote end of the link, or an active device becoming inactive.
These events can be used to control the authorization state of the Port and initiate the process of authenticating the attached device
if the Port is unauthorized. This is the Port-Based Network Access Control.
Port-Based Network Access Control
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Network access controlled port
Network access uncontrolled port
RADIUS
Server
Ethernet Switch
Figure 11- 10. Example of Typical Port-Based Configuration
Once the connected device has successfully been authenticated, the Port then becomes Authorized, and all subsequent traffic on
the Port is not subject to access control restriction until an event occurs that causes the Port to become Unauthorized. Hence, if the
Port is actually connected to a shared media LAN segment with more than one attached device, successfully authenticating one of
the attached devices effectively provides access to the LAN for all devices on the shared segment. Clearly, the security offered in
this situation is open to attack.