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Name: Joan P.
Status: Student
Age: 40s
Location: N/A
Country: N/A
Date: Around 2001

What is a firewall? I am assuming it has something to do with security and hacker prevention. I was hoping you could lead me to a good source for more information.

Firewalls come in many different forms, and can be hardware devices, or programs that are run on a server computer. They also do many different things, so this is going to be a really simplified version of things.

Firewalls basically are placed between a computer that wants to connect to the Internet and the actual connection to the Internet. Then, when a computer wants to connect to the Internet, its data goes through the firewall, and then to the Internet.

Likewise, someone on the Internet wants to connect to a computer, all of the data goes through the firewall, and then to the computer.

If a firewall simply passed every message along, it wouldn't be very useful. Typically firewalls do not simply pass every message along, and firewalls do several different things, but not every firewall does them all:
1. Filtering
2. Proxy Servers
3. Routing

1. A firewall can filter messages (packets) and decide whether to send them along or not. Firewalls can deny requests coming from the Internet. It can also deny requests going to the Internet. So, a firewall can block all messages coming from the Internet that do not match specific criteria. So if a request comes from an unknown source, it is denied. Since most hackers will be unknown, this prevents them from breaking in. Firewalls can also prevent certain types of data from going out. This helps prevent a virus or other unknown application from sending out data. The filtering can also stop things besides hackers. Firewalls can prevent specific applications from being used, both by people on the Internet or people behind the firewall.

2. A firewall can act as a proxy server. When set up this way, only the firewall can establish a connection on the Internet. The other computers can't. When they need to make an Internet connection, they contact the firewall, and tell it what they want to do. The firewall then establishes the connection and makes the request, and passes the results back. This provides several benefits. First, every computer that connects to the Internet needs an IP address, and they cost money. Since the firewall is the only computer connected, a company could buy a single IP address, and connect as many computers to the proxy server as they need. Second, since only the firewall is connected, the other machines are effectively invisible to computers on the Internet. This means the connection has to come from inside the firewall.

3. Routing. When a firewall is used as a proxy server, it is also acting as a router. This means that it is directing or routing network messages to the correct machines inside the network. Firewalls also can direct Internet traffic to specific machines inside the network. Doing this is sometimes called a hole in the firewall because now Internet traffic can connect to a machine on the other side of the firewall, if it follows the rules set up by the firewall.

In summary, firewalls simply determine how someone can use their computer to access the Internet, and how someone can use the Internet to access a computer inside the firewall. Because they can control access, they are mostly used for security purposes.

So, how do hackers get past a firewall? They find a hole and use it. A firewall is no good if it blocks everything, so a hacker finds something that is allowed to go through the firewall, and use that. For example, if a telecommuter can get through the firewall to access specific files, the hacker makes his Internet look like the telecommuter, and then can get in.

If you are still curious, there is a lot of good information on the Internet.

One site that has a lot of good links is:

Hope this helps,
--Eric Tolman

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