Transition Networks
S4224 Web User Guide
33558 Rev. C
Page 97 of 669
NAS Port Configuration
The table has one row for each S4224 port and a number of columns, which are explained below.
Port
The port number for which the configuration below applies. The * in the Port column acts as a ‘wild
card’ character which causes the selections in this row to be applied to all other rows in the table for
which this selection is valid.
Admin State
If NAS is globally enabled, this selection controls the port's authentication
mode. Note that the 802.1x Admin State must be set to
Force
Authorize
for
ports enabled for Spanning Tree. The Spanning Tree function is configured at
Configuration
>
Spanning
Tree
>
CIST
Ports
>
CIST
Normal
Port
Configuration
in the “STP Enabled” column.
The following modes are available:
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 802.1X, 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 (
). Frames sent between the switch
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
. 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 can get authenticated on the port at a
time. Normal EAPOL frames are used in the communication between the supplicant and the switch. If
