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Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter10 Configuring IEEE 802.1x Port-Based Authentication
Understanding IEEE 802.1x Port-Based Authentication
•Private VLAN—You can configure inaccessible authentication bypass on a private VLAN host port.
The access VLAN must be a secondary private VLAN.
•Voice VLAN—Inaccessible authentication bypass is compatible with voice VLAN, but the
RADIUS-configured or user-specified access VLAN and the voice VLAN must be different.
•Remote Switched Port Analyzer (RSPAN)—Do not configure an RSPAN VLAN as the
RADIUS-configured or user-specified access VLAN for inaccessible authentication bypass.
In a switch stack:
•The stack master checks the status of the RADIUS servers by sending keepalive packets.
When the status of a RADIUS server changes, the stack master sends the information to the stack
members. The stack members can then check the status of RADIUS servers when re-authenticating
critical ports.
•If the new stack master is elected, the link between the switch stack and RADIUS server might
change, and the new stack immediately sends keepalive packets to update the status of the RADIUS
servers.
If the server status changes from dead to alive, the switch re-authenticates all switch ports in the
critical-authentication state.
•When a member is added to the stack, the stack master sends the member the server status.
802.1x Authentication with Voice VLAN Ports
A voice VLAN port is a special access port associated with two VLAN identifiers:
•VVID to carry voice traffic to and from the IP phone. The VVID is used to configure the IP phone
connected to the port.
•PVID to carry the data traffic to and from the workstation connected to the switch through the IP
phone. The PVID is the native VLAN of the port.
The IP phone uses the VVID for its voice traffic, regardless of the authorization state of the port. This
allows the phone to work independently of802.1x authentication.
In single-host mode, only the IP phone is allowed on the voice VLAN. In multiple-hosts mode,
additional clients can send traffic on the voice VLAN after a supplicant is authenticated on the PVID.
When multiple-hosts mode is enabled, the supplicant authentication affects both the PVID and the
VVID.
A voice VLAN port becomes active when there is a link, and the device MAC address appears after the
first CDP message from the IP phone. Cisco IP phones do not relay CDP messages from other devices.
As a result, if several IP phones are connected in series, the switch recognizes only the one directly
connected to it. When 802.1x authentication is enabled on a voice VLAN port, the switch drops packets
from unrecognized IP phones more than one hop away.
When 802.1x authentication is enabled on a port, you cannot configure a port VLAN that is equal to a
voice VLAN.
When IP phones are connected to an 802.1x-enabled switch port that is in single host mode, the switch
grants the phones network access without authenticating them. We recommend that you use multidomain
authentication (MDA) on the port to authenticate both a data device and a voice device, such as an IP
phone.