LLDP and CDP

LLDP (Link Layer Discovery Protocol) and CDP (Cisco Discovery Protocol) are link layer protocols for directly connected LLDP and CDP capable neighbors to advertise themselves and their capabilities to each other. By default, the switch sends an LLDP/CDP advertisement periodically to all its interfaces and terminates and processes incoming LLDP and CDP packets as required by the protocols. In LLDP and CDP, advertisements are encoded as TLV (Type, Length, Value) in the packet.

The following are additional points about CDP/LLDP configuration:

NOTE     CDP/LLDP does not distinguish if a port is in a LAG. If there are multiple ports in a LAG, CDP/LLDP transmit packets on each port without taking into account the fact that the ports are in a LAG.

The operation of CDP/LLDP is independent of the STP status of an interface.

If 802.1x port access control is enabled at an interface, the switch will transmit and receive CDP/LLDP packets to and from the interface only if the interface is authenticated and authorized.

If a port is the target of mirroring, then for CDP/LLDP it is considered down.

NOTE     CDP and LLDP are link layer protocols for directly connected CDP/LLDP capable devices to advertise themselves and their capabilities. In deployments where the CDP/LLDP capable devices are not directly connected and are separated with CDP/LLDP incapable devices, the CDP/LLDP capable devices may be able to receive the advertisement from other device(s) only if the CDP/LLDP incapable devices flood the CDP/LLDP packets they receives. If the CDP/LLDP incapable devices perform VLAN-aware flooding, then CDP/LLDP capable devices can hear each other only if they are in the same VLAN. It should be noted that a CDP/LLDP capable device may receive advertisement from more than one device if the CDP/ LLDP incapable devices flood the CDP/LLDP packets.