IEEE 802.1x Authentication with MAC Authentication Bypass
You can configure the switch to authorize clients based on the client MAC address by using the MAC
authentication bypass feature. For example, you can enable this feature on IEEE 802.1x ports connected to
devices such as printers.
If IEEE 802.1x authentication times out while waiting for an EAPOL response from the client, the switch
tries to authorize the client by using MAC authentication bypass.
When the MAC authentication bypass feature is enabled on an IEEE 802.1x port, the switch uses the MAC
address as the client identity. The authentication server has a database of client MAC addresses that are allowed
network access. After detecting a client on an IEEE 802.1x port, the switch waits for an Ethernet packet from
the client. The switch sends the authentication server a RADIUS-access/request frame with a username and
password based on the MAC address. If authorization succeeds, the switch grants the client access to the
network. If authorization fails, the switch assigns the port to the guest VLAN if one is configured. This process
works for most client devices; however, it does not work for clients that use an alternate MAC address format.
You can configure how MAB authentication is performed for clients with MAC addresses that deviate from
the standard format or where the RADIUS configuration requires the user name and password to differ.
If an EAPOL packet is detected on the interface during the lifetime of the link, the switch determines that the
device connected to that interface is an 802.1x-capable supplicant and uses 802.1x authentication (not MAC
authentication bypass) to authorize the interface. EAPOL history is cleared if the interface link status goes
down.
If the switch already authorized a port by using MAC authentication bypass and detects an IEEE 802.1x
supplicant, the switch does not unauthorize the client connected to the port. When re-authentication occurs,
the switch uses the authentication or re-authentication methods configured on the port, if the previous session
ended because the Termination-Action RADIUS attribute value is DEFAULT.
Clients that were authorized with MAC authentication bypass can be re-authenticated. The re-authentication
process is the same as that for clients that were authenticated with IEEE 802.1x. During re-authentication, the
port remains in the previously assigned VLAN. If re-authentication is successful, the switch keeps the port
in the same VLAN. If re-authentication fails, the switch assigns the port to the guest VLAN, if one is configured.
If re-authentication is based on the Session-Timeout RADIUS attribute (Attribute[27]) and the
Termination-Action RADIUS attribute (Attribute [29]) and if the Termination-Action RADIUS attribute
(Attribute [29]) action is
Initialize
(the attribute value is
DEFAULT
), the MAC authentication bypass session
ends, and connectivity is lost during re-authentication. If MAC authentication bypass is enabled and the IEEE
802.1x authentication times out, the switch uses the MAC authentication bypass feature to initiate
re-authorization. For more information about these AV pairs, see RFC 3580,
“
IEEE 802.1X Remote
Authentication Dial In User Service (RADIUS) Usage Guidelines.
”
MAC authentication bypass interacts with the features:
•
IEEE 802.1x authentication
—
You can enable MAC authentication bypass only if 802.1x authentication
is enabled on the port .
•
Guest VLAN
—
If a client has an invalid MAC address identity, the switch assigns the client to a guest
VLAN if one is configured.
•
Restricted VLAN
—
This feature is not supported when the client connected to an IEEE 802.lx port is
authenticated with MAC authentication bypass.
•
Port security
•
Voice VLAN
Catalyst 2960-X Switch Security Configuration Guide, Cisco IOS Release 15.0(2)EX
290
OL-29048-01
Configuring IEEE 802.1x Port-Based Authentication
IEEE 802.1x Authentication with MAC Authentication Bypass
