Troubleshooting At The Physical Level

Thought it would be a good idea to start a series using the NetworkDataPedia’s theme of ‘knowing your network. Let’s start at layer 1 or the hardware layer.

Unfortunately there is so much that can go wrong at this layer but you will still have a network connection and life will seem fine. I say unfortunately because if the problems would cause an complete outage, you would be forced to address it.

I find that many physical level issues are grouped into a few categories:

Installation and Support

I have many issues caused by installation, support shortcuts. Heres a quick list of what I’ve seen; CAT5 cable wrapped around a welder, RJ45 couplers to combine 2 short cables, unsupported bundle of cables pulling the RJ45 connectors out from the switch, overheating modem in a plastic bag, dirty fibre optic cables and ports.

And that’s just what I can remember at the moment. I’m sure you have a bunch yourselves.

Inheritance

Many times analysts build on to an existing system not knowing or understanding the whole picture. A great example is where I saw half the cable run using shielded twisted pair cabling and the new run was unshielded. When I asked why they wouldn’t continue the shielded cabling, the contractor said, ”no one uses that stuff anymore”. Unfortunately I checked the entire run of shielded cables and in my opinion shielded cabling was required. The client brushed it off and I found out later they had to change the cabling due to ‘excessive errors on the new cable runs’. Oops

When possible, the best way to start at the physical layer is to ‘go for a walk’. Either follow a connection from a host to the network, or verify the installation documentation. In this day of video conferencing and smartphones, you can even do this remotely by having someone walk around with their phone.

I have learned a lot working on ‘network cleanups’ network migrations and installations since there is always a surprise to overcome.