Black Box LPB2910A, User Manual

Page: 80 / 367

Publication date: Sept, 2015
Revision A1
68
Once the switch considers whether to enter the Guest VLAN, it will first check if this option is
enabled or disabled. If disabled (unchecked, default), the switch will only enter the Guest VLAN if
an EAPOL frame has not been received on the port for the lifetime of the port. If enabled (checked),
the switch will consider entering the Guest VLAN even if an EAPOL frame has been received on the
port for the lifetime of the port.
The value can only be changed if the Guest VLAN option is globally enabled.
 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 that the configuration below applies to.

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: 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
N
OTE
: 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 ongoing 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.