Transition Networks
SISGM
–CHAS L2/L3 Switch User Guide
33625 Rev. B
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5.8.5 NAS (802.1x)
This page allows you to configure the IEEE 802.1X and MAC-based authentication system and
port settings.
The IEEE 802.1X standard defines a port-based access control procedure that prevents
unauthorized access to a network by requiring users to first submit credentials for authentication.
One or more central servers (the backend servers
)
determine whether the user is allowed access
to the network. These backend (RADIUS) servers are configured on the
Configuration
>
Security
>
AAA
page.
MAC-based authentication allows for authentication of more than one user on the same port, and
does not require the users to have special 802.1X software installed on their system. The switch
uses the users' MAC addresses to authenticate against the backend server. As intruders can
create counterfeit MAC addresses, MAC-based authentication is less secure than 802.1X
authentication.
Overview of 802.1X (Port-Based) Authentication
In an 802.1X network environment, the user is called the supplicant, the switch is the authenticator,
and the RADIUS server is the authentication server. The switch acts as the man-in-the-middle,
forwarding requests and responses between the supplicant and the authentication server. Frames
sent between the supplicant and the switch are special 802.1X frames, known as EAPOL (EAP
Over LANs) frames which encapsulate EAP PDUs (RFC3748). Frames sent between the switch
and the RADIUS server are RADIUS packets. RADIUS packets also encapsulate EAP PDUs
together with other attributes like the switch's IP address, name, and the supplicant's port number
on the switch. EAP is very flexible as it allows for different authentication methods, like
MD5-Challenge, PEAP, and TLS. The important thing is that the authenticator (the switch) does
not need to know which authentication method the supplicant and the authentication server are
using, or how many information exchange frames are needed for a particular method. The switch
simply encapsulates the EAP part of the frame into the relevant type (EAPOL or RADIUS) and
forwards it.
When authentication is complete, the RADIUS server sends a special packet containing a success
or failure indication. Besides forwarding the result to the supplicant, the switch uses it to open up
or block traffic on the switch port connected to the supplicant.
Note: in an environment where two backend servers are enabled, the server timeout is configured
to X seconds (using the authentication configuration page), and the first server in the list is
currently down (but not considered dead), if the supplicant retransmits EAPOL Start frames at a
rate faster than X seconds, it will never be authenticated because the switch will cancel on-going
