How to debug network connection?

Question

^{Typical dialog with no explanation why can't windows connect.}

Sometimes it happens that you can't connect to certain router. How can I obtain some verbose info about connection procedure to find out what went wrong?

Is there a command line version of the network connection UI?

Answer 1

This article gives good overview on diagnosing network problems on Windows: http://technet.microsoft.com/en-us/magazine/ff625276.aspx

It starts with GUI methods you probably tried, but then touches on netsh (Network Shell) which is very powerful command line utility. It allows you to control everything network related (command reference); in particular it provides tracing with netsh trace context (command reference). Netsh can include windows events and network traffic in it's traces as well as plethora of additional diagnostic information.

You may also combine both methods (quoted from technet article):

When you enable tracing with Netsh.exe, Windows 7 can create two files. An ETL file contains trace events for Windows components, and if specified, network traffic. By default, the ETL file is named Nettrace.etl and stored in the %TEMP%\NetTraces folder. You can specify a different name and storage location with the tracefile= parameter. An optional CAB file can contain several types of files including text, Windows Registry, XML and others that store additional troubleshooting information. The CAB file also includes a copy of the ETL file. By default, the CAB file is named Nettrace.cab and stored in the %TEMP%\NetTraces folder.

You can also use Netsh.exe tracing in conjunction with Control Panel | Troubleshooting. First, use the appropriate Netsh.exe command to enable tracing for the scenario. For example, use the netsh trace scenario=internetclient report=yes command. Use Control Panel | Troubleshooting to run the Connect to the Internet troubleshooting session. When complete, run the netsh trace stop command. Now, when you view the history of the troubleshooting session, you’ll be able to access the CAB file.

Answer 2

I understand you need to have a tool to troubleshoot network in general. In this case you can get a lot of network-related information by using tcpdump or Wireshark if you want a nice GUI.

Answer 3

The command you're referring to is called "ipconfig".

It will tell you if you get an ipaddress from the router and if so, what it is.

If you get an 169.254.?.? address, it basically says: this computer wants to get an IP address from a DHCP server, but no DHCP server gave an ip address.

This can be due to not being able to reach the router, or the router's dhcp not working properly, or all slots have been taken.

If you do get an ip address from the router, or you have a static one, the next step is to ping the router to see if you can get a connection between you and the router. If so, ping the internet both by an url and by an ip address, for example 8.8.8.8

Lastly, determine if there are more computers in the network who have network issues.

Also, physically look at the network connector that goes into the computer. There are 2 lights. A green and Orange one. Both should be blinking. If not, something is wrong with the cable or its not connected properly, or the device at the other end does not provide any network activity. (a hub that lost power for example)

I can go into far more details, but that would make this way too broad for the scope of SuperUser.