[Davehc]

One of my ralations is an executive in an Internet Security organisations. I copied this from a very large write up which they issue to potential customers:


Chances are, if you are a small business, you may not even need a firewall. If you are using a dial-up modem connection, or are using an on-demand ISDN connection to the internet, a firewall is usually not necessary. This is because your internet connection is only operating when you need it. If your internet connection is down, then an outsider has no way of connecting to your LAN via the internet, and so a firewall is unnecessary.

Here's an example to illustrate this point. Let's assume that your office has an internet access appliance such as Webramp or Netopia. When someone on your LAN needs to access the internet (i.e., to browse a web page, fetch e-mail, etc.), it brings your internet connection up, and then drops it once the connection is no longer needed. This minimizes the cost of your internet connection, and it also makes it very difficult for an outsider to connect to your computers. Not only must he correctly guess the IP address of your machine (it often varies from session to session with dial-up and ISDN connections), but he must also have guessed your user account and password, AND he must correctly guess exactly when you have an active connection to the internet. If you are an occasional internet user, and your connection is down most of the time, it will be very difficult for somebody to compromise your computer if you are using a dial-up connection.
If you have a dedicated internet connection, one which is up 24 hours a day, then putting a firewall in place is probably a good idea since a hacker could systematically try to break into your machines in the early morning hours when you are least likely to detect it. (Most break-ins usually go undetected unless the intruder damages or erases files from a machine).
Selecting a firewall
I recommend buying a router that has a firewall built into it. This is usually the most cost-effective solution, is easy to set up and administer, and does not require the purchase of superfluous hardware. If you already have a router in place, a stand-alone firewall may also be a good idea, especially now that low-cost turnkey units are starting to appear. Unless you are an expert in networking software, I generally don't recommend software-based firewalls. Most router vendors now offer basic firewall services either as a basic feature or as an optional upgrade. Ascend, for example, has a firewall upgrade for their Pipeline 50 series of ISDN routers. It only adds a small amount of cash or so to the cost of the router, and so it's a great value compared to buying a standalone appliance.