Black Box LPB2910A, User Manual

Page: 81 / 367

Publication date: Sept, 2015
Revision A1
69

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 the 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.
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 Port
Security Limit Control.

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 in the 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 using the Port Security Limit Control functionality.