Link Layer Discovery Protocol (LLDP) is the open source answer to Cisco’s proprietary Cisco Discovery Protocol (CDP). LLDP is specified in IEEE 802.1AB and is similar to CDP in many ways. Let’s take a look at LLDP in action, and see what you may need to do to make it work with other vendors’ devices.
My Arista 7124S switch is connected to a Cisco 3750. The connection is between G1/0/52 on the 3750 and e24 on the Arista. When I turn up the port, I get the following message on the Arista console:
Apr 10 23:21:35 Arista Lldp: %LLDP-5-NEIGHBOR_NEW: LLDP neighbor with chassisId 001c.b084.cfb4 and portId "[ Arista e24 ]" added on interface Ethernet24
Without configuring anything, the Arista switch has discovered the Cisco switch, even though the Arista switch is not running CDP. Let’s dig in and see what Arista sees:
sho lldpLLDP transmit interval : 30 seconds LLDP transmit holdtime : 120 seconds LLDP reinitialization delay : 2 seconds Enabled optional TLVs: Port Description System Name System Description System Capabilities Management Address (best) IEEE802.1 Port VLAN ID IEEE802.3 Link Aggregation IEEE802.3 Maximum Frame Size Port Tx Enabled Rx Enabled Et1 Yes Yes Et2 Yes Yes Et3 Yes Yes Et4 Yes Yes Et5 Yes Yes Et6 Yes Yes Et7 Yes Yes Et8 Yes Yes Et9 Yes Yes Et10 Yes Yes Et11 Yes Yes Et12 Yes Yes Et13 Yes Yes Et14 Yes Yes Et15 Yes Yes Et16 Yes Yes Et17 Yes Yes Et18 Yes Yes Et19 Yes Yes Et20 Yes Yes Et21 Yes Yes Et22 Yes Yes Et23 Yes Yes Et24 Yes Yes
That’s pretty ...