CDP/LLDP Neigbor Details

[Lesley Ngwetsana]

Hi Team,

Two switches are connected to each and that link is a trunk port between those two switches, The challenge is on one switch when I perform cdp/lldp neigbor detail I can see the other switch which is connected to it but funny thing when I ping it, it's unreachable.

What causes this. Please help.

[MHM Cisco World]

It real connect if you see other SW in cdp' but that not meaning it have l3 reachability.

Show ip route 

Check which subnet is appear in both SW and use it to ping 

MHM

[paul driver]

Hello
CDP is a L2 protocol, it has not bearing on the reachability to the switch, The cdp messages will advertise the first active ip address on the switch - reachable or not

[Joseph W. Doherty]

As both the others have noted you don't have L3 reachability and as Paul has noted CDP (and LLDP) operate at L2.  Just wanted to add L3 reachability might be due to reasons beyond L3 routing such as L3 security.  I.e. even if the two devices IPs are in the same subnet pings could be blocked.

[Richard Burts]

My colleagues have provided good explanation about how CDP operates at layer 2 and does not reflect anything about layer 3. If we are to assist in investigating this issue we need more information. As a start please post the output of show cdp neighbor detail (if possible post output from both switches). In particular we will want to see which interfaces are being used. Then please post the output of show ip interface brief (from both switches if possible) so that we can understand what IP is associated with the interface. Then please post the output of show arp (from both switches if possible). Hopefully this information will allow us to find the issue. If not then we will need to request additional information.