Tuesday, January 10, 2012 - 14:57
A simple firewall uses rules based on virtual 'ports' and IP addresses to filter traffic. Most Internet applications and services have well known ports on which machines 'listen' for communications (as standardised by the Internet Assigned Numbers Authority (IANA)). Firewalls will generally be configured to block anything by default but then allow traffic to flow through certain ports, either to and from any IP address or to a subset of IP addresses.
