Everything you wanted to know about Firewalls (but were afraid to ask)

Organizations are increasingly relying on the Internet to perform their day-to-day business.  As an organization’s Internet use has increased most companies have moved away from dial-up connections to cable, DSL, and T1 (broadband) connections that are always connected to the Internet.  While these connections offer substantial performance improve-ments they also expose the computer network to a greater risk of outside intrusion.

     This greater risk has given rise to the increased importance of protecting data, electronic services, and property from being stolen, damaged, or misused.  One way to increase network security is to use a firewall.  A firewall provides a boundary between a private network such as your LAN (Local Area Network) and the outside world.  Firewalls help promote security by acting as a gateway through which all traffic moving in and out of the network must pass.

     A firewall is configured to filter packets, i.e. to let certain ones through and block all others.  The most basic filtering is done by allowing or denying packets based on the source or destination IP address.  The next level of filtering is done on the “ports” required for a particular application (e.g.: www, FTP, telenet) to operate.

     No firewall is hack proof but if your firm only permits outbound requests (i.e. does not host a web site, FTP site, permit remote access to email, etc.), you can really make your environment secure by only permitting packets in which are in response to your own outbound requests.       

     There are two styles of firewalls, software and hardware.  Software firewalls consist of software that is loaded on a server on your network and then configured.  A very popular software firewall program is Microsoft’s ISA Server.  Software solutions allow for greater expandability and control however can also have more vulnerabilities.  A hardware firewall is an additional piece of hardware that is connected between the external router and LAN.  Hardware firewalls, also known as Firewall Appliances, have become more popular recently because of their affordability, ease of installation, and ease of monitoring.

     Within these styles, firewalls can differ widely in the level of protection, features that they offer, and price.  Some of these features are closely related to a protection function whereas others have been bundled for convenience.

     Almost all firewalls feature user definable logging of normal or suspicious events to serve as an audit trail.  Many firewalls have intrusion and attack detection to protect your network against denial -of-service attacks where your router is flooded with so much data that valid users cannot get through.

     Some of the services are those more traditionally associated with routers such as internet connection sharing or VPN’s.  If a hard drive is available, caching and reverse caching can be enabled to store commonly accessed data for faster access.

     Some services offered on firewalls replace traditional standalone products such as web content filtering (prevent access to undesirable web sites), email content filtering (scan email for certain words, content, or attachments), SPAM filtering (to help eliminate the dozens of unsolicited emails a person might receive each day), and Antivirus filtering (to prevent files with viruses from even entering the network). 



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