What is firewall ?

A firewall is a piece of hardware or software that helps prevent malware and malicious attacks from entering a computer or a network of computers through the Internet.
Firewalls have been a first line of defense in network security for over 25 years. They establish a barrier between secured and controlled internal networks that can be trusted and untrusted outside networks, such as the Internet.
A firewall can be hardware,software or both.

Hardware firewalls

Hardware firewalls are systems that are independent of the computers they protect that filter the Internet as information passes into a computer.
Most broadband Internet routers have their own firewall built in.
In general, hardware firewalls work by examining the data that flows in from the Internet and verifying whether that information is safe.
The ZyXEL ZyWALL, which is a Unified Security Gateway with a firewall and other security features.
Cost: $100 to ~$500
NAT, DCHP, Email Notification.
Easier for computers to locally share folders/Printers.
Additional function available & can protect other devices.

Software firewalls are designed to protect a computer by blocking certain programs from sending and receiving information from a local network or the Internet.
The Windows Firewall, an example of a firewall software program included with Microsoft Windows.
Cost: Free to $30 per computer.
Each machine need to be configured.
Firewall may be interfere with local network sharing.