53
1.877.877.2269
BLACKBOX.COM
NEED HELP?
LEAVE THE TECH TO US
LIVE 24/7
TECHNICAL
SUPPORT
1.877.877.2269
CHAPTER 2: CONFIGURATION
Port Configuration
The table has one row for each port on the selected switch and a number of columns, which are:
Port: The port number for which the configuration below applies.
Admin State: If NAS is globally enabled, this selection controls the port’s authentication mode. 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 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).
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 piggyback 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 more than one supplicant is connected to a port, the one that comes first
when the port’s link comes up will be the first one considered. If that supplicant doesn’t provide valid credentials within a certain
amount of time, another supplicant will get a chance. Once a supplicant is successfully authenticated, only that supplicant will be
allowed access. This is the most secure of all the supported modes. In this mode, the Port Security module is used to secure a
supplicant’s MAC address once successfully authenticated.
Multi 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 piggyback on the successfully
authenticated client and get network access even though they really aren’t authenticated. To overcome this security breach, use the
Multi 802.1X variant.
Multi 802.1X is really not an IEEE standard, but features many of the same characteristics as does port-based 802.1X. Multi 802.1X
is—like Single 802.1X— not an IEEE standard, but a variant that features many of the same characteristics. In Multi 802.1X, one or more
supplicants can get authenticated on the same port at the same time. Each supplicant is authenticated individually and secured in the
MAC table using the Port Security module.
