Publication date: June, 2015
Revision A1
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 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 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 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.
In Multi 802.1X it is not possible to use the multicast BPDU MAC address as destination
MAC address for EAPOL frames sent from the switch towards the supplicant, since that
would cause all supplicants attached to the port to reply to requests sent from the switch.
Instead, the switch uses the supplicant's MAC address, which is obtained from the first
EAPOL Start or EAPOL Response Identity frame sent by the supplicant. An exception to this
is when no supplicants are attached. In this case, the switch sends EAPOL Request Identity
frames using the BPDU multicast MAC address as destination - to wake up any supplicants
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