Firewalls: Definition

This motivation brings us to the discussion of firewalls.

The term firewall, in the real world, means a wall that was built to protect from fire and intended to slow the spread of fire through a structure.

The same concept is used in networks too: a network firewall is intended to stop unauthorized users from accessing the network and its services from other external networks. Specifically, a firewall is a combination of software and hardware that decides what kinds of connection requests and what specific data packets can pass to and from a computer or a local network.

The most common deployment of firewalls is between a trusted network of an organization to an untrusted network (typically the Internet) as shown on the next slide. Typically, the Internet Service Provider (ISP) connection terminates at a border router and then connects to a firewall.