A firewall is a computer security device that is situated between a small business's internal network and the Internet. It can work at either the software or the hardware level to prevent unwanted outside access to the company's computer system. The firewall basically acts as a guard, identifying each packet of information before it is allowed to pass through. It is one of the most effective forms of protection yet developed against hackers operating on the Internet. Setting up a firewall has distinct advantages and disadvantages.
Advantages
A firewall blocks "evil packets" from being "permitted to reach a place where they can do harm," says Terry Gray, Chief Technology Architect for the University of Washington. The key issue is not whether to block harmful packets, but where to block them. The individual system's operating system-based firewall can be configured to provide a great deal of security, but a network-based firewall, such as a router, can protect multiple systems simultaneously.
Disadvantages
Packet filtering by a software firewall can degrade your system's performance, because it's a demanding task to examine every packet of data. A hardware firewall eases this burden.
Whichever option you choose, configuring and maintaining the firewall can be a difficult maintenance chore. A network firewall also can lend users a false sense of security, encouraging them not to maintain security at the machine level. If the network firewall fails or is not configured properly, this could prove disastrous.