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What's a firewall?
A firewall is like a doorman who keeps unwanted people out of a building.
Imagine that you are at home, using your laptop, and you want to use a computing service that's at the University. When your laptop tries to contact the University computer, its network traffic has to cross the internet, then go through the University's firewall computers.
The job of these firewall computers is to allow through only legitimate, harmless-looking traffic. Unwanted network traffic is not passed through, so it never arrives at the University computers.
This filtering of network traffic is called a firewall. All network traffic to the University is either allowed through the firewall, or is blocked by it. Computers which are protected by a firewall are said to be behind the firewall.
Holes in the firewall
A firewall has to be told which network traffic it should allow through. If it's told to allow (for example) web traffic to a certain University computer, that's known as a hole in the firewall. Firewall holes allow us to run services such as websites on our computers, and make them visible to the whole world, even when the computer running the website is behind the firewall.
About our firewalls
The University of Edinburgh has a firewall, and it protects the entire University network.
Although the School of Informatics is part of the University of Edinburgh, it has its own distinct computer network, with its own firewall to protect it. This firewall keeps a lot of unwanted traffic out of the Informatics network. Another page gives more technical information about our firewall:
The Informatics network is part of the University of Edinburgh network - so the Informatics firewall is inside the University firewall.
VPN - another way through a firewall
Using a VPN can allow you through a firewall. If you use the University VPN on your computer, you will be allowed through the University firewall.
If you use the Informatics VPN, you will be allowed through both the University firewall and the Informatics firewall. (Usually you won't need to use the Informatics VPN, because what you need to use will already be available by other means.)
See also our page on VPNs.