Nov102011

Why do my client PCs lose their Internet connections after I turn on a firewall?

Gebrehiwot asks:

I am using Windows Server 2003 on my LAN as a domain controller and active directory. It is also a DHCP server. I have 30 computers with Windows 7 connected via switches. When I try to connect these clients to the Internet it works, but if I turn on the firewall, the Internet will stop working after a period of time on the clients (but not the server). Any ideas on how to fix this?



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4 Answers -

0 votes

Jeff Fabish

November 11, 2011

Hi Gebrehiwot,

What firewall are you using? You may want to use a third party firewall, I believe Windows Server 2003′s firewall only performs inbound filtering

Anyway, the most common cause of this is because you haven’t added an exception to a server or port. You must configure a policy to allow TCP & UDP port 80 inbound and outbound. 

0 votes

Mike

November 11, 2011

As Jeff said it would be good to know which Firewall you are using.

If you are using Microsoft ISA Server make sure to add all necessary protocols to the rules and set them as allowed.

Bare minimum should be HTTP (Port 80), HTTPS (Port 443), DNS (Port 53), DHCP Reply (Port 67 UDP). At best you do this via “Add Protocols > All Protocols” and then select the corresponding ones.

You will also want to run gpupdate via command line otherwise it may take 5-30 minutes for the rules to finally apply.

0 votes

Anonymous

November 11, 2011

How to configure Windows Server 2003 SP1 firewall for a Domain…
http://support.microsoft.com/kb/555381

0 votes

Aibek

November 12, 2011

Hi Gebrehiwot,

Were you able to fix the issues using suggestions above? Let us know.