A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. If an incoming packet of information is flagged by the filters, it is not allowed through
Without a firewall in place, all of the computers on your company network are directly accessible to anyone on the Internet. Someone who knows what they are doing can probe those computers, try to make FTP connections to them, try to make telnet connections to them and so on - If one employee makes a mistake and leaves a security hole, hackers can get to the machine and exploit the hole.
A firewall implements security rules. For example, one of the security rules might be:
Only one computer is permitted to receive public FTP traffic - Allow FTP connections only to that one computer and prevent them on all others.
A company can set up rules like this for FTP servers, Web servers, Telnet servers and so on. In addition, a firewall can control how network users connect to Web sites, whether files are allowed to leave the company over the network and so on. A firewall gives a company tremendous control over how people use the network.
Firewalls use several methods to control traffic flowing in and out of a network:
Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded.
Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa.
Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information.
Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded |
