Troubleshooting applications which operate across WAN (wide area networks) can be especially difficult. When a PC has the potential to both communicate with servers and other workstations across different IP networks and subnets there will almost always be complications. The PC could be using various methods and protocols to communicate and there’s inevitably the difficulty of identifying if your network hardware or the end network is causing the problems.
It’s important before looking for complex solutions is to start with the basics. A computer that needs to communicate across a wide area network will normally be configured to route it’s traffic through a default gateway. Although it sounds unlikely, misconfiguration of this very basic setting is quite often the root cause of any network connectivity issue. Basic IP configuration on the workstation will break most connectivity, remember it may be some external change that has caused this problem too. If a router or gateway is removed or updated, then any static configurations must be updated.
The error could be a simple incorrect IP address of the default gateway, or more commonly something like a incorrect subnet mask. Always remember that many operating systems require a reboot to enforce changes in IP configuration, another simple mistake to make especially if diagnosing remotely. If you can talk to a user or have command access on the workstation, the first checks should be basic connectivity ones. If a workstation can ping hosts on the same subnet but not on other subnets, your next step should be to check connectivity to the default gateway.
Other errors can be simply down to incorrect name resolution. If all network configuration and operation is ok, then it may simply be that the machine is being directed to the wrong address. Static information for name resolution can unfortunately be stored in all sorts of places, some difficult to locate. There are files on the host PC which should be checked both hosts and lmhosts can cause connectivity issues if there’s an incorrect address. Also many devices cache addresses to help with speed and network connectivity.
Checking IP connectivity might not tell the whole story though particularly if you’re trying to troubleshoot an application. Many have their own connectivity and configuration information pre-installed, a configuration files with incorrect connectivity information. These could potentially overwrite things like a default gateway and cause issues. Many applications work through web browsers and can also pick up connection details from these, users will offer specify a proxy in their browsers settings for various reasons, perhaps for accessing a popular web site like BBC iPlayer from abroad – such as this http://bbciplayerabroad.co.uk/which would also cause the application to be routed through the proxy too. It may work ok depending on the configuration of the proxy server (many just pass through data like this) however it will have an extra step added to the route.