CDP & LLDP Explained: Discovering Network Neighbours
CDP and LLDP are neighbour-discovery protocols: they let a device learn what's directly connected to each port — device name, model, IP and interface. CDP is Cisco-proprietary; LLDP is the open standard (802.1AB) used across vendors.
What they reveal
show cdp neighbors (or show lldp neighbors) is a first stop in troubleshooting — it confirms which switch/router port connects where without tracing cables. Add detail to see IP addresses and IOS versions. Invaluable when documenting or debugging an unfamiliar network.
Security note
Because these protocols advertise device details, it's good practice to disable them on ports facing untrusted devices or the internet (an attacker could learn your topology). Enable them internally for operations, disable them at the edge — a small but real security habit covered in CCNA and CyberOps.
Frequently asked questions
What is the difference between CDP and LLDP?
CDP is Cisco-proprietary; LLDP (802.1AB) is the open, multi-vendor standard. Both discover directly connected neighbours and their details.
What information does CDP provide?
Neighbour device name, hardware model, connected local and remote interfaces, and (with detail) IP address and software version.
Should CDP be disabled anywhere?
Yes — on ports facing untrusted networks or devices, since it advertises information an attacker could use to map your topology.
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