User manual

APS User Manual
277
frame when the port link comes up, and any client on the port will be
allowed network access without authentication.
Force Unauthorized: In this mode, the switch will send one EAPOL Failure
frame when the port link comes up, and any client on the port will be
disallowed network access.
Port-based 802.1X: In the 802.1X-world, the user is called the supplicant,
the switch is the authenticator, and the RADIUS server is the authentication
server. The authenticator 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. EAPOL frames
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, in that it
allows for different authentication methods, like MD5-Challenge, PEAP, and
TLS. The important thing is that the authenticator (the switch) doesn't 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 this decision to
the supplicant, the switch uses it to open up or block traffic on the switch
port connected to the supplicant
NOTE: Suppose two backend servers are enabled and that the
server timeout is configured to X seconds (using the AAA
configuration page), and suppose that the first server in the list is
currently down (but not considered dead).
Now, if the supplicant retransmits EAPOL Start frames at a rate
faster than X seconds, then it will never get authenticated, because
the switch will cancel on-going backend authentication server
requests whenever it receives a new EAPOL Start frame from the
supplicant.
And since the server hasn't yet failed (because the X seconds
haven't expired), the same server will be contacted upon the next
backend authentication server request from the switch. This