How do you diagnose network issues on Windows?

Question

I often run into problems where I can't get something to connect to something else. I usually forget to check something obvious. Can you help with:

• A tip/technique for diagnosing a connection issue
• The name of a tool or application that can help (and the situation in which it's useful)

I know the question is a little non-specific, but hopefully the answers can form a useful starting point for anybody who's stuck trying to get computers/programs talking to each other.

Please can you give one answer per answer so the best ones can be voted up.

Answer 1

Simple checks to run when debugging network problems:

1. Has each machine got an IP address, Go to command prompt and run ipconfig. Key things to check here are the interfaces and ensuring the appropriate ones have IP addresses.
2. Check both machines IP addresses are in the same range and subnet if you are running it on an internal or Virtual network.
3. Try pinging each machine from the other to see if they can communicate with each other. Note that some firewalls will block ping requests.
4. If Pinging fails then check to see if firewalls are active. If the communication is within a 'safe' internal network then try disabling the firewalls and re-pinging.
5. If the connections are over a wireless network then check signal strength.
6. If pinging fails and you are connecting through several networks then try running a tracert to see at which will may show you where on the network the connection is failing.
7. If you are able to ping but not connect then check firewall settings and network connection settings. Windows 2000+ has the capability of setting port an ip access on a connection properties.
8. Try drawing a network diagram of the connections to help in visualising the problem.
9. If you are connecting through routers, firewalls and loadbalancers then check that all devices are not tied to any specific ip addresses and that the IP address redirection (if in place) is correct. Also check any NAT logs to see if connections are being received and properly re-directed.

Answer 2

Wireshark

Latest versions of ProcMon

netstat