Mor, on Firewalls
Subtitle: Your network should have a doorman, and the firewall is it.
There are two basic types of firewalls, software and hardware. The primary difference is that a software firewall runs as software on the computer it is protecting. A hardware firewall exists as a separate piece of hardware that sits between the 'outside' and the system or systems it is protecting.
For a simple home setup, high-speed internet and a single computer for example, I recommend having both. The hardware firewall will intercept and drop the majority, if not all, of the invalid entries to your computer. This will keep the activity of your software firewall to a minimum, allowing your computer to spend it's time doing something you find productive. The software firewall, which is not likely to be of the same design as the hardware firewall, acts as a second layer of defense, picking off what the hardware firewall isn't designed to.
The good news is most modern operating systems now include a software firewall. It's free, and allowing ligitimate traffic through when you add services to your network is often automatic. Third party software firewalls may not be as automatic, but there may be features that make it worthwhile to get. Features of software firewall is really a different article.
Hardware firewalls can come in a number of forms.
When you purchase a consumer router, you typically are getting three different network devices in one. A firewall, a router, and a switch. One low cost (typically under $100); one low power device (typically up to twelve volts DC and two amps or less for twenty-four watts or less).
The majority of internet service providers out there will include only one external IP address in the basic service they provide. This is where routing comes in. Including routing in the same box as does the firewalling adds only a little overhead, as it has to process the packets that come in or go out anyways. Routing when you only have one external IP address involves Network Address Translation (NAT). Big technical words. NAT works like adding a name to the address on a piece of standard mail. The post office knows where your address is, but has no idea who is living there.
An ethernet switch allows multiple ethernet devices (computers, printers, etc) to connect with out having to have a wire running from each device to each of the other devices.
Commercial firewalls are usually standalone devices that just keep the outside out, and inside in. Commercial firewalls are also processing allot more traffic than your average consumer box.
It is also possible to repurpose an older computer system as a firewall. There are a number of bootable CDs and even bootable floppies that run Unix style operating systems such as Linux, NetBSD, FreeBSD, and OpenBSD. With varying levels of knowledge, it is also possible to take a default installation of one of these operating systems and roll your own hardware firewall.
On a network of two or more computers the software firewall between each computer and your network is not just added protection between the computer and the internet. Malicious software (of the virus, worm, spyware, or adware varieties) have a number of ways of spreading from computer to computer. If the malicious software (malware) is downloaded from a web site using a pathway you have to open up between your firewalls and the outside world, obviously it's going to get onto your system. Once the malware is on a system, it may still try and spread to other computers on your network using more indirect methods. The software firewall can protect against this kind of spread. Properly configured, both the hardware and software firewalls can prevent malware from sending information back to the internet you don't want to get there.
Software firewalls are often included as part of a suite of security software, this may include anti spyware, anti virus, anti spam, and privacy protection software. These are the security patrol and house keeper to the door man that is the firewall.
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