Application Guide

[67]
Software User's
Manual
–
Version 3.0
Admin State
If NAS is globally enabled, this selection controls the port’s authentication mode.
Setting Description
Force
Authorized
In this mode, the switch will send one EAPOL Success 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 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