Possibly broken switch ports, how to diagnose?

Question

Preface: We have some weird behaviour in our home network. Some connections established seem to be rather unstable, but we still don't know, if the DSL-router or other components are the culprit.

To track the issue down I have to do it step by step. In the middle of all, there's a 24 port 1000 Mbps HP V1910-24G managed switch. In the switch cabinet there's a grounded patch panel supplying 16 RJ45-ports to all rooms with minimum CAT 6 cabling (not sure if CAT 7, but length is short, so it doesn't matter much). The cabling is not only used to distribute ethernet but also S0-Bus for telephony. It is very well possible that this switch has suffered some damage as someone may have accidentally connected a S0-Bus-line to a switch port.

The management interface of the switch doesn't show any problems, and connections on the ports are reflected by the status LEDs.

I have different computers (Win, Mac, Linux) but no dedicated network measurement equipment. I think I will start digging into iperf3 doku. Is this tool the right tool to detect issues with switch ports? And are there other means to find out if switch ports are not operating properly?

Answer 1

The easiest approach is to test a switch port with a directly connected laptop. If it links at full speed it's likely OK. Run a performance test with a known-good partner (e.g. using iperf3) to make sure.

If the port doesn't link at full speed, check its config and admin status (enabled/disabled). If all that looks fine but there's no link, the port is dead.

You might want to mark damaged port to avoid them in the future. You can use 8P8C dust caps or simply cut-off plugs from old patch cables. Also, you might want to use a different color for the ISDN patches.

If a port has been tested good but still performs poorly in real use your cabling is likely faulty. You can check the runs with the above method, even without the switch.