Firewall Breakdown

By Joshua Erdman
Digital Foundation, inc.

With so many firewall terms, how does one know what type of firewall they need? What is the difference between a packet filtering firewall and a NAT firewall? How much security does one need?

A Firewall's Purpose

Firewalls protect data and computing resources, they are also limit access for users; bottom line it is your network security and survelience system. This article will help you determine just how much security you need.

Brush up on those skills

To prepare to make a good choice about the levels of protection you need to be very familiar with some network basics. First, brush up on the first 3 layers of the 7-layer OSI model. You also need to read our article on TCP/IP which discusses general TCP/IP usage and also read TCP/IP addresing. It covers addressing schemes and subnet masks and ports.

The thing that makes administrating firewalls difficult is that traffic ALWAYS flows in both directions. Even though you want your users to browse the Internet you must let the websites that they want to browse reply back in some way so that they can send the user the content of the website. So in general we want to block incoming requests by default and allow outgoing requests incoming replies.

Assumptions

Typically most networks have all the client PCs configured with a private network address (192.168.0.X OR 10.10.0.X) and the local network uses the Internet connection by being shared through a DSL/Cable Router. This is commonly referred to as a NAT Firewall (one of the most basic). Yes those users who wanted to share their Internet connection are actually protected by a NAT firewall and didn't even know it.

All of our firewall articles listed below are going to assume the internal office network is using private addresses. If firewalls are new to you, I recommend reading up on the first articles to get a good understanding of how they protect.

Levels of Protection and complexity

NAT - Outbound Only
NAT - using Port Forwarding for incoming connections
Packet Filtering
IDS (Intrusion Detection AKA:Stateful Inspection)
Audit Trails

Article last reviewed: 06/27/2004

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Created by: Digital Foundation, inc.

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