Lantech LGS-2624C, User Manual, Page: 220 / 279

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 that might be on the port.
The maximum number of supplicants that can be attached to a port can be
limited using the Port Security Limit Control functionality.
MAC-based Auth.
Unlike port-based 802.1X, MAC-based authentication is not a standard, but
merely a best-practices method adopted by the industry. In MAC-based
authentication, users are called clients, and the switch acts as the
supplicant on behalf of clients. The initial frame (any kind of frame) sent by
a client is snooped by the switch, which in turn uses the client's MAC
address as both username and password in the subsequent EAP exchange
with the RADIUS server. The 6-byte MAC address is converted to a string
on the following form "xx-xx-xx-xx-xx-xx", that is, a dash (-) is used as
separator between the lower-cased hexadecimal digits. The switch only
supports the MD5-Challenge authentication method, so the RADIUS server
must be configured accordingly.
When authentication is complete, the RADIUS server sends a success or
failure indication, which in turn causes the switch to open up or block traffic
for that particular client, using the Port Security module. Only then will
frames from the client be forwarded on the switch. There are no EAPOL
frames involved in this authentication, and therefore, MAC-based
Authentication has nothing to do with the 802.1X standard.
The advantage of MAC-based authentication over port-based 802.1X is that
several clients can be connected to the same port (e.g. through a 3rd party
switch or a hub) and still require individual authentication, and that the
clients don't need special supplicant software to authenticate. The
advantage of MAC-based authentication over 802.1X-based authentication
is that the clients don't need special supplicant software to authenticate.
The disadvantage is that MAC addresses can be spoofed by malicious
users - equipment whose MAC address is a valid RADIUS user can be
used by anyone. Also, only the MD5-Challenge method is supported. The
maximum number of clients that can be attached to a port can be limited