252CDP compatibility enables a switch to use LLDP to perform the following tasks:• Receive and recognize the CDP packets from the directly-connected device.• Send CDP packets to the directly-connected device.The packets that the switch sends to the neighboring CDP device carry the device ID, the ID of the portconnecting to the neighboring device, the port IP address, the PVID, and the TTL. The port IP address isthe primary IP address of the VLAN interface in up state. The VLAN interface must have the lowest VLANID among all VLANs permitted on the port. If none of the VLAN interfaces of the permitted VLANs isassigned 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-informationcommand show the CDP neighboring device information that can be recognized by the switch. For moreinformation about the display lldp neighbor-information command, see Layer 2—LAN SwitchingCommand Reference.Configuration prerequisitesBefore you configure CDP compatibility, complete the following tasks:• Globally enable LLDP.• Enable LLDP on the port connecting to a device supporting CDP.• Configure LLDP to operate in TxRx mode on the port.Configuration procedureCDP-compatible LLDP operates in one of the following modes:• TxRx—CDP packets can be transmitted and received.• Disable—CDP packets cannot be transmitted or received.LLDP traps are sent periodically, and the interval is configurable.To make CDP-compatible LLDP take effect on a port, follow these steps:1. Enable CDP-compatible LLDP globally.2. Configure CDP-compatible LLDP to operate in TxRx mode on the port.The maximum TTL value that CDP allows is 255 seconds. To make CDP-compatible LLDP work correctlywith Cisco IP phones, configure the LLDP frame transmission interval to be no more than 1/3 of the TTLvalue.To enable LLDP to be compatible with CDP:Step Command Remarks1. Enter system view. system-view N/A2. Enable CDP compatibilityglobally. lldp compliance cdp By default, CDP compatibility isdisabled globally.3. Enter Layer 2/Layer 3 Ethernetinterface view ormanagement Ethernetinterface view.interface interface-typeinterface-number N/A
