Niveo Professional NGSME16T2H - Manual (Page 76)

Chapter 3: Featuring Configuration – Web UI
Featuring Configuration – Web UI
NGSME16T2H User Manual | 76
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 scenario will loop forever.
Therefore, the server timeout should be smaller than the supplicant's EAPOL Start
frame retransmission rate.
Single 802.1X
In port-based 802.1X authentication, once a supplicant is successfully authenticated
on a port, the whole port is opened for network traffic. This allows other clients
connected to the port (for instance through a hub) to piggy-back on the successfully
authenticated client and get network access even though they really aren't
authenticated. To overcome this security breach, use the Single 802.1X variant.
Single 802.1X is really not an IEEE standard, but features many of the same
characteristics as does port-based 802.1X. In Single 802.1X, at most one supplicant