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

Gebrehiwot November 10, 2011
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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?

  1. Aibek
    November 12, 2011 at 3:48 pm

    Hi Gebrehiwot,

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

  2. Anonymous
    November 11, 2011 at 8:21 am

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

  3. Mike
    November 11, 2011 at 6:40 am

    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.

  4. Jeff Fabish
    November 11, 2011 at 5:05 am

    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.