Link Layer Discovery Protocol
LLDP is an industry standard protocol (IEEE 802.1AB).
It is usually disabled on Cisco devices by default, so it must be manually enabled.
A device can run CDP and LLDP at the same time.
LLDP messages are periodically sent to multicast MAC address 0180.C200.000E.
When a device receives an LLDP message, it processes and discards the message. It does not forward it to other devices.
By default, LLDP messages are sent once every 30 seconds.
By default, the LLDP holdtime is 120 seconds.
LLDP has an additional timer called the 'reinitialization delay'. If LLDP is enabled (globally or on an interface), this timer will delay the actual initialization of LLDP. 2 seconds by default.
Configuration commands
LLDP is usually globally disabled by default.
LLDP is also disabled on each interface by default.
To enable LLDP globally:
R1(config)# lldp runTo enable LLDP on specific interfaces (tx):
R1(config-id)# lldp transmitTo enable LLDP on a specific interface (rx):
R1(config-id)# lldp receiveConfigure the LLDP timer:
R1(config-id)# lldp timer <seconds>Configure the LLDP holdtime:
R1(config-id)# lldp holdtime <seconds>Configure the LLDP reinit timer:
R1(config-id)# lldp reinit <seconds>
Show basic information about LLDP (timers, version).
R1# show lldpDisplays how many LLDP messages have been sent and received.
R1# show lldp trafficDisplays which interfaces LLDP tx/rx is enabled on.
R1# show lldp interfaceLists LLDP neighbors and some basic information about each neighbor.
R1# show lldp neighborsLists each LLDP neighbor with more detailed information.
R1# show lldp neighbors detailsDisplays the same info as above, but for the specified neighbor only.
R1# show lldp entry <name>Wireshark capture
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