wall.
The firewall determines which inside services may be accessed from the outside, which outsiders are permitted access to the inside services and which outside services may be accessed by insiders. For a firewall to be effective, all traffic to and from the Internet must pass through the firewall, where it can be inspected. The firewall must permit only authorized traffic to pass, and the firewall itself must be immune to penetration. Unfortunately, a firewall system cannot offer any protection once an attacker has gotten through or around the firewall.
It is apparent from the discussion so far, that firewalls would be a big business, and most experts estimate that companies spend more than a billion dollars a year on firewall software and other Internet security systems. All security experts agree that firewalls, in and of themselves, are useless unless they are used as a part of a comprehensive data security policy that includes:
* Published security guidelines to inform users of their responsibilities
* A network access policy, service access policy
* Established local and remote user authentication policies
* Secure dial-in and dial-out policies
* Policies covering disk and data encryption, virus protection and employee security checks.
Without a firewall, each system of a private network is exposed to attacks from other hosts on the Internet. This means the security of the private network would depend on the "hardness" of each host's security features and is only as safe as the security of the weakest system.
A firewall program enables the network administrator to define a centralized "choke point" that keeps unauthorized users (i.e., hackers, crackers, vandals and spies) out of the protected network, prohibits potentially vulnerable services from entering or leaving the protected network and provides protection from various types of muting
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