156Automatically identifying IP phones through LLDPWhen you use OUI addresses to identify IP phones, the number of OUI addresses that can be configuredis limited. Additionally, when there are plenty of IP phones in the network, you must configure many OUIaddresses. If your IP phones support LLDP, you can configure LLDP to automatically identify IP phones. Formore information, see "Enabling LLDP to automatically discover IP phones."Configuring a device to advertise voice VLANinformation to IP phonesHow a device advertises voice VLAN informationWhen an IP phone supports LLDP, the device can advertise the voice VLAN information to IP phonesthrough the LLDP-MED TLVs.When an IP phone supports CDP rather than LLDP, you can configure CDP compatibility to enable thedevice to advertise the voice VLAN information to IP phones through the CDP packets.For more information about LLDP and CDP compatibility, see "Configuring LLDP."How a device obtains voice VLAN information• Configuring a voice VLAN on ports. For more information, see "Configuring a voice VLAN on aport."• When an IP phone cooperates with the authentication function, the server-assigned VLANinformation can be advertised to the IP phone. For more information, see "Dynamically advertisingserver-assigned VLANs through LLDP."• Configuring LLDP to advertise the specific voice VLAN information. For more information, see"Configuring LLDP to advertise a specific voice VLAN."Figure 50 shows the order of the three methods.Figure 50 Workflow of advertising voice VLAN information to IP phones
