There are various types of firewall. In ascending order, they are…

* Packet layer- This analyses network traffic at the transport protocol layer.

* Circuit level- This validates that packets are either connection or data packets.

* Application layer- This ensures valid data at the application level before connecting.

* Proxy server- This intercepts all messages entering or leaving the network.

In the real world, threats have evolved over the years and firewalls have evolved to deal with them. While it is still possible to buy packet only firewalls, they are not adequate for business use. Protection against combination threats is best provided by firewalls which combine all of the above elements.

Specific functions performed by firewalls include:

* Gateway defense

* Carrying out defined security policies

* Segregating activity between your trusted network, the Internet and your DMZ (a protected zone midway between your network and the Internet, where you would perhaps have your web or email server)

* Hiding and protecting your internal network addresses (NAT)

* Reporting on threats and activity  

What firewalls don’t do

Even with a firewall, there are still many areas of risk for your network. The most obvious is malware. Malware is a combination of the words ‘malicious’ and ‘software’ and includes viruses, trojan horses, worms, spyware/adware, phishing and pharming. Malware is most commonly acquired through clicking on email attachments and email links.    

Viruses, trojans and worms can cause a range of symptoms from the annoying and/or embarrassing to the much more serious which can affect the functioning of your business. Spyware/adware gathers information about you. It can record keystrokes and, as such, can potentially be very dangerous, revealing everything you do on your computer.

Another well-known threat, not covered by your firewall, is SPAM. Dealing with SPAM can seriously affect your productivity and, as SPAM often contains viruses and phishing emails, it is also a direct security threat.

Phishing is about fake emails trying to extract sensitive information, such as your bank passwords or credit card details and a variation of this is pharming, where the criminal sets up a fake web site which looks like one you normally use, typically a banking site. Once you enter your details, the criminal is able to plunder your account.

Many people are also unaware that you can actually acquire malware by simply browsing web sites. This is a rapidly growing threat and some of the malware is used to create Botnets. Some security applications (e.g. those from Finjan) have a facility which protects you against websites containing malware, by checking the sites before you click on them.

Another danger to your network is from a DDoS (distributed denial of service) attack. This is a malicious attempt to prevent an organization being able to use its Internet based systems by flooding them with emails until the servers are overwhelmed. These attacks are often carried out by BotNet networks of compromised PCs, which are also used in SPAM campaigns. Specific DDoS software can guard against this threat.

Other dangers to your network include unauthorized access, and the way to deal with this is to have proper authentication procedures in place, for both local and remote access. In many cases, passwords are not enough and the use of strong authentication with tokens provides much better security.

Further potential problems are from data theft or leakage, for example when a laptop is stolen. The answer here is to encrypt all sensitive data. Low cost solutions are available. Finally all wireless use is risky and requires a specific wireless firewall, and wireless VPN for remote access.

A firewall is no longer enough to protect a company network. Other security solutions to combat the threats outlined above are also necessary, as well as proper staff training.

One of the best ways to protect against the main threats not covered by a firewall is to use a UTM (unified threat management) device. UTM devices are multi-purpose security solutions which have a minimum of a firewall, VPN, anti-virus and intrusion detection/prevention. Some UTMs (sometimes known as super UTMs) also incorporate capabilities such as web filtering (blocking problematic web sites), SPAM blocking and spyware protection.

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