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Communication Problems between computers on switched network

Posted on 2015-02-03
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Last Modified: 2015-02-05
I have a single subnet network that consists of two buildings. One building has a has a Netgear FS726T Smart switch and the other has a Netgear FS750T2 Smart switch. The two switches are connected by fiber. The server on the network is a Windows 2008 SBS which hosts the DNS and DHCP servers. This setup has worked fine for the past five years. Suddenly, yesterday, five computers where not able to connect to the servers, internet etc. I tried restarting all the equipment with no success. This morning, they are suddenly able to connect again. However, there are still communication issue between some computers. For example, I am not able to ping some of the computers in building two but I am able to ping my computer from those machines. I am at a loss as to what to check. Any suggestions?
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Question by:Robcarter10
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Qlemo earned 2000 total points
ID: 40586726
The latter might result from Windows Firewall reactivating or switching back to not allow incoming connections. A ping from those machines will work then, but not to them.

Yesterday, has there been anything those 5 machines had in common? Were they on the same building, same switch?
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by:Robcarter10
ID: 40586750
They were on the same switch in the same building. There was a variety of Firewalls and OS involved. There was not policy changes made to any of these machines. I have been able to remote desktop to all of these machines in the past. My initial thought is that it is the switch but I do not know what a switch would stop allowing data to certain ports.
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by:Qlemo
ID: 40586794
Ports can get blocked by a managed switch if there is too much going wrong on that port. Broadcast storms, loops, hardware protocol errors, for example. This could effect other ports as well, but would than count as failure of the switch.

See if you can get device and port statistics from that switch, in particular error counts.
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by:Robcarter10
ID: 40587112
I tried disabling the firewall on one of the computers that i cannot ping and was able to ping it. I didn't even consider this to be an option because I have not changed any configuration on the firewall and have never had an issue connecting to those machines. Not to mention, some of them are running different AV/Firewall. I still don't know if this would have caused the issue I had yesterday though where the computers were not able to access anything on the network at all. Unfortunately, I was off sick so I could not try that and they were working before I arrived today.
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