We have a network with 100 computers (HP Desktops with Windows 7 Pro) all connected through Cisco Switches. We have a Windows Server 2003/2008R2 domain.
About two weeks ago, a problem started happening where a couple of computers, sometimes only one, will drop off the network. Is happening for one computer much more than others. Can happen multiple times a day. Can happen for multiple computers at same time, but can also happen at different times. The computers this is happening on are connected to different Cisco Switches. When it happens for one computer, other computers conntected to the same switch are not affected. All computers are connected, through ethernet, to a Cisco IP Phone which has two ethernet ports on the back. One for the wall and one for the computer. When the problem happens, the Cisco IP phone is not effected at all.
When I say "drop off the network" here is what I mean:
The user complains that they have no internet and what ever program they are in says "Not Responding". A lot of the times it is a network program they are working in, but sometimes it will just be MS Word 2010.
Upon diagnosing the computer, an ipconfig will show everything is normal. Computer has IP Address, Default Gateway, Subnet, DNS's etc. I ping the gateway but there is no response. I ping 127.0.0.1 and it works fine. I ping the computers IP and it works fine.
After performing a reboot, the problem will go away, most of the time. The one time I saw where the problem did not go away, the computer assigned a 169.x.x.x IP address.
Another way that I have fixed the problem is by performing a "Windows Network Diagnostics" and the troubleshooter finds this problem: "The default gateway is not available". The troubleshooter then disable and re-enable the network card and this fixes the problem. The troubleshooters details of this problem is in the attached word document. The doc refers to an ETL file for its diagnostics. You have to download Microsoft's Network Monitor program to read this file. Did that but I couldn't find anything useful as it didn't give much information. I would upload it but ETL's are not allowed on experts-exchange.
Yet, another way I have fixed this problem is by running the command: netsh winsock reset. I did this along with a few other commands and rebooted the computer. Not sure if the commands fixed it or if it was simply the reboot.
Once the problem is fixed, no matter how I fixed it, it will stay fixed for a while but can return at anytime, one hour or one day or one week.
I've contacted our Cisco Support Company and they can't find any problems with the Cisco Switches. No logs show any problems.
Where do I go from here to try an figure out the cause of this problem?