Administrator Guide

708 VLANs
Identifying Voice Traffic
Some VoIP phones contain full support for IEEE 802.1X. When these phones
are connected to a port that uses 802.1X port-based authentication, these
phones authenticate and receive their VLAN information from LLDP-MED.
However, if a VoIP phone has limited support for 802.1X authentication it
might try to authenticate and fail. A phone with no 802.1X support would not
attempt to authenticate at all. Instead of placing these phones on an
unauthenticated or guest VLAN, the switch can automatically direct the VoIP
traffic to the Voice VLAN without manual configuration.
The switch identifies the device as a VoIP phone by one of the following
protocols:
• Cisco Discovery Protocol (CDP) or Industry Standard Discovery Protocol
(ISDP) for Cisco VoIP phones
• DHCP vendor-specific options for Avaya VoIP phones
• LLDP-MED for most VoIP phones
After the VoIP phone receives its VLAN information, all traffic is tagged with
the VLAN ID of the Voice VLAN. The phone is considered to be authorized
to send traffic but not necessarily authenticated.
Segregating Traffic with the Voice VLAN
The switch can be configured to support Voice VLAN on a port that is
connected to the VoIP phone. Both of the following methods segregate the
voice traffic and the data traffic in order to provide better service to the voice
traffic.
• When a VLAN is associated with a Voice VLAN port instead of an 802.1p
priority, then the VLAN ID information is passed onto the VoIP phone
using either the LLDP-MED or the CDP protocol, depending on how the
NOTE: Voice VLAN must be configured on general mode ports. It is not
supported on access mode or trunk mode ports.
NOTE: By default, ISDP is enabled globally and per-interface on the switch.
LLDP-MED is disabled on each interface by default. Port-based authentication
using 802.1X is also disabled on each port by default.