There are a couple of basic commands to diagnose a network problem that every network admin needs to know. Let’s get down to the nitty gritty.
You have an issue with a computer on your network. It cannot connect to the internet and doesn’t have any network resources. The first thing you need to do is check the condition of the physical connection i.e. the network cable. After that is secured, I jump to a command prompt and do a IPCONFIG /all like so:
I check that the IP address, default gateway and subnet mask are all correct. If they are not, I make my modifications and we are back online. Too bad the problems don’t usually go away that easily. Next up, I attempt to ping the servers by IP address using the ping command, like so:
Now I check for DNS issues by pinging the server’s name. If this fails, it is our internal DNS issue and I know where to move on to.
If I get a correct response, I try to ping a website like www.google.com. That tests external DNS resolution. If that works as well, the trouble runs deeper. I would then run a Netstat ““a and see who is connected to my machine and determine if maybe a Trojan or virus has gained control of it.
Everything looks clean. Now I would try pathping or tracert between the machine and the internet to diagnose any remaining network problems. This one I will not show you as all the output would reveal my network settings and what not. I am not looking to create more problems!
During your tests you might conclude that another machine is using the same IP address or host name as your desktop and causing issues. For this, I would recommend using Angry Ipscanner.exe (found here here) to query for that IP address or the entire network to find the host name”¦
I have been using this application for more than a decade to diagnose network problems! If you cannot figure out what is going on and why you cannot get to the resource you are trying to, then the issue might be network-related and has nothing to do with your machine. First, check if you can get to the resource from a different machine.
Then it might be time to fire up Wireshark (which used to be called Ethereal, covered here for you old schoolers). Wireshark will listen to your network adapter for all traffic and responses. The answer is in the data but you do need to know how to read it. There are lots of good resources online or you could always come knocking at AskTheAdmin’s door with your output and ask us to help!
How would you troubleshoot a fidgety connection? Do you have any secret commands?