I want to start with a couple of cautionary tales which show the importance of not taking anything for granted when troubleshooting network problems.

The first involves a notebook PC which I need to connect to my wireless network at home ­ a fairly simple procedure and one I’ve completed successfully many times. This time, however, it didn’t go so smoothly.

Connecting the notebook to my wireless router was easy enough. It was running Vista and had an 802.11g Wifi interface built-in, so as soon as I booted it I was presented with a list of available wireless networks. I selected my own, typed in the appropriate encryption key, and the notebook was given an IP address in exchange, enabling me to start browsing the web.

When I tried to connect to my Network Attached Storage (Nas) appliance, however, I couldn’t see it. Indeed, as far as the notebook was concerned it was the only other device on the Lan, apart from the router.

I then made a fundamental mistake and began troubleshooting the problem at the notebook end without checking anything else, starting with the settings in the Vista Network and Sharing Center. However, all seemed in order and none of the changes I made had any effect.

My next thought was that it was something to do with firewall, so I disabled this, but no change. Even when I disabled other security software on the notebook and re-booted, just in case, I still couldn’t see anything on the network.

Finally I went into the room where the Nas appliance was located and found that it was powered off, as was my network printer and almost every other device on the network. And then I remembered the electrician who had been in earlier and had needed to turn the power off to install a new light ­ although I have UPS (Uninterruptible Power Supply) protection for one or two key devices, the Nas box isn’t one of them.

Had I made this check first I could have saved 30 minutes of fiddling. Of course I could also have pinged the Nas appliance first to make sure it was there, but that too can be misleading. As in my second cautionary tale, involving a device that appeared to be on the network but, in reality, wasn’t.

Playing ping pong
I was called in to troubleshoot an issue with a network device attached to a photocopier. Whenever the copier was used it would prompt the user for an account code. It would then log that information, together with the number of pages being copied, to a network database. Customers could then be charged for any copies made on their behalf.

The company (an engineering firm) had installed two of these devices and configured both with appropriate IP addresses using the management software provided. One was working correctly but the other was reported as disconnected. Moreover, although it was possible to ping both devices, they were only able to telnet into one, the other simply refusing the remote connection.

This time I started with the basics and physically disconnected the problem device from the network ­ only to discover that I still got a response when I pinged its address.