Configuring a Cisco Router Flashcards
What is CDP and what is LLDP?
CDP - Cisco Discovery Protocol
-only supports Cisco devices
LLDP - Link Layer Discovery Protocol
-vendor neutral version of CDP
Both CDP and LLDP are used as a network discovery tool.
They also are a carrier / communication tool that can work with TLV (Type, Length, Value) fields to neighboring devices.
Example - When a device is plugged into a switch and needs PoE supplied power, LLDP is the protocol that allows that negotiation to happen.
What are the commands to configure CDP globally and on specific interfaces?
At the global config you can run either:
cdp run
no cdp run
At the interface config you can run either:
cdp enable
no cdp enable
What is the difference in configuration of LLDP vs. CDP and the commands to configure?
The main difference in configuration is that you must have LLDP enabled globally and then you can specify the ports that have it enabled or disabled. By default, after LLDP is enabled globally, all ports are enabled for transmit and receive.
From the global config:
[no] lldp run
From the interface config:
[no] lldp transmit
[no] lldp receive
What is the command to check the specific settings of CDP and LLDP, such as how often their advertisements are sent out?
show cdp
show lldp
What are the commands for checking for neighboring devices with CDP and LLDP?
show cdp neighbors (detail)
show lldp neighbors (detail)
NOTE - If you are not seeing any expected cdp or lldp neighbors, it’s possible that the other device(s) have cdp and/or lldp disabled on their interfaces.
