There are a number of basic design issues that should be addressed by the lucky person who has been tasked with the responsibility of designing, specifying, and implementing or overseeing the installation .of a firewall
The first and most important decision reflects the policy of how your company or organization wants to operate the system: is the firewall in place explicitly to deny all services except those critical to the mission of connecting to the Net, or is the firewall in place to provide a metered and audited method of ``queuing'' access in a non-threatening manner? There are degrees of paranoia between these positions; the final stance of your firewall might be more the result of a political than an engineering decision.
مقاله انگلیسی Firewalls