Configuring CDP compatibility
When the switch is directly connected to a Cisco device that supports only CDP rather than LLDP, you can enable CDP compatibility to enable the switch to exchange information with the directly-connected device.
CDP compatibility enables the switch to use LLDP to receive and recognize CDP packets from the directly-connected device and send CDP packets to the directly-connected device. The packets that the switch sends to the neighboring CDP device carry the following information:
Device ID.
ID of the port connecting to the neighboring device.
port IP address.
PVID.
TTL.
The port IP address is the primary IP address of the VLAN interface in up state. The VLAN ID of the VLAN interface must be the lowest among the VLANs permitted on the port. If no VLAN interfaces of the permitted VLANs is assigned an IP address or all VLAN interfaces are down, no port IP address will be advertised.
The CDP neighbor-information-related fields in the output of the display lldp neighbor-information command show the CDP neighboring device information that can be recognized by the switch. For more information about the display lldp neighbor-information command, see Layer 2—LAN Switching Command Reference.
If your LLDP-enabled device cannot recognize CDP packets, it does not respond to the requests of Cisco IP phones for the voice VLAN ID configured on the device. As a result, a requesting Cisco IP phone sends voice traffic without any VLAN tag to your device. Your device cannot differentiate the voice traffic from other types of traffic.
CDP compatibility enables your device to receive and recognize CDP packets from a Cisco IP phone and respond with CDP packets carrying TLVs with the voice VLAN configuration. According to TLVs with the voice VLAN configuration, the IP phone automatically configures the voice VLAN. As a result, the voice traffic is confined in the configured voice VLAN and is differentiated from other types of traffic.
For more information about voice VLANs, see "Configuring voice VLANs."