Web and XML Glossary

A Firewall is a special kind of Gateway that is used to block certain types of network traffic (typically, network traffic that is potentially dangerous). Most Firewalls work as packet filters, comparing the passing packets to a set of filter rules. Typically, the comparison performed by the packet filter involves the source address, the source Port, the destination address, and the destination Port. Filtering on source and destination addresses grants control over who may communicate with the internal network. All traffic from undesirable networks can be screened out. Ports, on the other hand, are used to distinguish network services. By filtering out a Port, it is possible to deny the outside world access to a service offered on the internal network.