Technology: Switching
Area: Neighbor Discovery
Vendor: Cisco
Software: 12.X , 15.X
Platform: Catalyst Switches, Most platforms

LLDP (Link Layer Discovery Protocol ) is a neighbor discovery protocol that is used for network devices to advertise information about themselves to other devices on the network. This protocol runs over the data-link layer.

Details, such as device capabilities or device identity can be advertised using this protocol. You can configure the frequency of LLDP updates, the amount of time to hold the information before discarding it or the initialization delay time. You can also select the LLDP TLVs for sending and receiving. Let’s take a look at LLDP configuration example for Cisco.

By default LLDP is disabled globally on Cisco devices. To enable it issue:

Switch# configure terminal
Switch(config)# lldp run

To configure a holdtime of 120 second, a delay time of 2 seconds and an update frequency of 30.

Switch# configure terminal
Switch(config)# lldp holdtime 120
Switch(config)# lldp reinit 2
Switch(config)# lldp timer 30 

To transmit LLDP packets only:

Switch# configure terminal
Switch(config)# no lldp receive

To receive LLDP packets:

Switch# configure terminal
Switch(config)# lldp receive

To globally disable LLDP.

Switch# configure terminal
Switch(config)# no lldp run

Disabling and Enabling LLDP on an Interface – LLDP is disabled globally on all supported interfaces. You must enable LLDP globally to allow a device to send LLDP packets.

Switch# configure terminal
Switch(config)# interface GigabitEthernet 1/1
Switch(config-if)# lldp transmit
Switch(config-if)# lldp receive
Switch(config-if)# end