Firewalls.

                Introduction to firewalls

A firewall is a hardware or software system that prevents unauthorized access to or from a network. It can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet. All data entering or leaving the intranet pass through the firewall, which examines each packet and blocks those that do not meet the specified security criteria.

Generally, firewalls are configured to protect against unauthenticated interactive logins from the outside world. This helps prevent hackers from logging into machines on your network. More sophisticated firewalls block traffic from the outside to the inside, but permit users on the inside to communicate a little more freely with the outside.

Firewalls are essential since they provide a single block point, where security and auditing can be imposed. Firewalls provide an important logging and auditing function; often, they provide summaries to the administrator about what type/volume of traffic has been processed through it. This is an important benefit: Providing this block point can serve the same purpose on your network as an armed guard does for your physical premises. 

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