Configuration optimization techniques for firewalls can be divided into two groups: general best practices and vendor-specific, model-specific configurations. This article will focus on best practices. The following are eleven best practices for firewall administrators to use to optimize firewalls for better performance and throughput.
Best practice No. 1: Ensure outbound traffic is compliant with policies
Remove bad traffic and clean up the network. Bad traffic includes non-compliant, unauthorized or undesired traffic. Notify server administrators about servers hitting the firewall directly with outbound denied Domain Name System (DNS), NTP, SMTP, HTTP and HTTP Secure (HTTPS) requests, as well as dropped/rejected internal devices. The administrators should then reconfigure the servers not to send this type of unauthorized outbound traffic (thereby taking load off the firewall).
Best practice No. 2: Filter unwanted traffic on the router(s) instead of the firewall
Move the filtering rules for unwanted inbound traffic from the firewall to the edge router(s) to balance the performance and effectiveness of the security policy. To do this, first identify the top inbound dropped requests that are candidates to move upstream to the router as Standard Access Control List (ACL) filters. This can be a time-consuming process but it is a good method for moving blocks upstream to the router, thus saving firewall CPU and memory.
Then, if you have an internal choke router between your network and firewall, consider moving common outbound traffic blocks to your choke routers. This will free more processing on your firewall.
Best practice No. 3: Remove unused rules and objects
Remove unused rules and objects from the rule bases. While cleaning up an unwieldy rule base might sound like a daunting task, there are a variety of automated tools available that can assist with rule cleanup. These automated tools make firewall policy management a much more manageable endeavor.
Best practice No. 4: Reduce rule base complexity
Reduce rule base complexity and rule overlapping should be minimized. Again, there are tools available that can dramatically reduce the time and headache involved in cleaning up and simplifying the rule base.