Firewall in Windows XP with Service Pack 2

Windows XP with Service Pack 2 has a built in firewall, which protects your computer against attacks from other computers on the internet and prevents unauthorized programs from gaining access to the internet from your computer. This feature is by default turned on, however you must always ensure that your version of Windows is updated, and patched. More information on how to do this can be found here.

Note: The firewall will not detect or remove any viruses. Therefore it is important to have an updated anti-virus program installed. F-Secure Anti Virus is available for students and employees at NTNU. More information can be found here, as well as an installation guide.

Firewall functions

When another computer tries to establish a connection with your computer, the firewall will automatically block this connection. However some programs are dependant on these connections to function properly. In these cases the firewall will ask which actions you wish to take regarding the link. You are given three options;Keep Blocking, Unblock and Ask Me Later.

1. The option Keep Blocking the firewall will deny the program to establish contact with the internet (and another machine).
2. The option Unblock will allow the program to establish a connection to the internet. The firewall will create a permanent exemption for this program, so the next time this program tries to connect to the internet, the firewall will let it through.

Firewall settings

At a later stage you might want to change the settings of your firewall. One example can be a program that you have previously let go through that you now wish to block.

Choose Start -> Settings -> Control Panel and double click on Windows Security Center. then click on Windows Firewall.

General

The tab General gives you the option to turn the firewall on and off. If you tick the box marked Don't allow exceptions, the firewall will block all programs from establishing contact with the internet (note that you can mark some programs to be excepted under the exceptions tag - see below).

Note; It is not recommended to turn the firewall of. However if you chose to do so, it is important to bear in mind that this will imply that your computer is much more prone to malicious attacks. It should however not be necessary to turn off the firewall, as it can easily be adapted as we shall see in the chapter below.

Exceptions

If you want the firewall to deny a program that you previously excepted, you can remove this program from the list under the tab Exceptions. Click on the program that you want to remove and click delete.

If you are experiencing problems with certain programs (they cannot access the net even if they are on the exception list) you can try to open a port manually. You do this by clicking Add port and typing in the number on the port you wish to open, and for which protocol (TCP or UDP)