Network Security: Firewalls

What is the purpose of a Firewall?

Firewalls are absolutely vital for keeping network security in force. The firewall stops and controls the traffic that comes between your network and the different sites you go to. A firewall is a constituent of a company's network protection, and it acts to keep in force the network security policy. It can log inter-network activity with efficiency. It can also reduce a network's vulnerability. Whenever an organization is connected to the Internet but is not using a firewall, any host on the network has direct access to all resources on the internet. If you don't have a firewall, every host online can attack every host in your network.

What is a Firewall Incapable of Doing?

Firewalls can't always detect malicious data. For the most part they cannot offer any protection against an attack from inside, although they may log network activity should the criminal use the Internet gateway. A connection that doesn't go through a firewall cannot be protected by a firewall. To put it another way, if you connect directly to the internet via modem, there is no way the network firewall can protect you. Some firewalls cannot protect from viruses. Firewalls also cannot totally protect against previously unknown attacks; while a simple firewall provides little protection against computer viruses.

Firewall User Authentication or Verification

You establish a claimed identity's validity via user authentication. The use of a password and user name can provide this authentication; however, it is not really strong authentication. When you use a public connection, for example if you have a connection to the Internet that is not encrypted, your user name and password can easily be copied by other people and replayed. Powerful user authentication makes use of cryptography, for example SSL certificates. A certificate of this sort can prevent "replay attacks" from occurring. A replay attack happens when a user name and password are captured and used again to gain unauthorized access.

Firewall-to-firewall encryption

A connection that is encrypted is sometimes called a VPN, or Virtual Private Network. Cryptography makes this more or less private. Of course it isn't really private. The information may be private but it is sent on a public network -- the Internet. While VPNs were available before firewalls were, they became more common when they began running on firewalls. Today, most firewall vendors offer a VPN option.

Additional Purposes of Firewalls

• Increasingly, firewalls are being used for purposes of content filtration. Virus scanning is a common addition to firewalls in this area as well. Though this may be a waste of resources, because filtering for viruses needs to be carried out by every computer since information might be transmitted to these computers via routes besides through the firewall itself - for example, via separate disks.
• URL Screening: Firewall regulated accessibility to the internet as well as content filtering of both files and messages appears to be a practical extension of a firewall. The drawback of utilizing a firewall for URL or content filtering is minimized performance.
• To restrict the size of network space that any single user can occupy, or restrict the amount of the network's bandwidth that may be utilized for given purposes.