Layer 2 troubleshooting

Layer 2 troubleshooting starts with checking the cables. This may seem obvious but is a step that many hardened engineers can miss, making the assumption that everything is cabled correctly. 

Assuming that everything is connected correctly, we can move on to some basic checks.

How to do it...

1. We can check that we can see the neighboring devices using some show commands:

      show cdp neighbors
      show lldp neighbors

Link Layer Discovery Protocol (LLDP) is vendor neutral, whereas Cisco Discovery Protocol (CDP) is proprietary to Cisco, so depending on the makeup of the fabric, one will be more applicable at times then the other.

2. We can check the status of a particular interface from the GUI by navigating to Fabric | Inventory | Pod 1 | Leaf-1 | Interfaces | Physical Interfaces, selecting the interface, and looking at the LLDP Neighbor field.

3. This does not give us much information, though, and we need to know which interface to select (there may be lots of them in your...