Dissecting Big Firewall Rules

A while back, I worked with one of our clients who was put in a tough spot by their external auditors. The auditor flagged every firewall rule that accepted traffic and used the “Any” object in the service column as non-compliant. Our client, in turn, asked us, “How can we quickly redefine these rules with more appropriate access? And how can we do it without interrupting business operations?” The answer we gave them was FireMon’s Traffic Flow Analysis.

Finding Big Rules

We’ve all had those handful of rules that we hate. They’ve been in the firewall for years and nobody remembers who put them there or why. But they all have something in common: they aren’t secure. They allow too much access, auditors hate to see them and no one can justify the access because the uses are too broad. Class A networks in the source or destination, “Any” objects in the service column, and the use of deeply nested group objects are all examples off broad access.

So, why were the rules added in the first place? There are a lot of reasons, but I think the most common one is that the real requirement for access was not well defined, so broad access was given to ensure functionality. It’s certainly not uncommon for security to be the last to know about architecture projects or new systems being deployed on the network, so engineering on a short timeline without all of the information has almost become status quo. Given the high probability of those scenarios continuing to occur, how can we improve the rule set without interrupting normal operations?

Removing Big Rules

FireMon’s Traffic Flow Analysis can help you pare down those big rules into a handful of manageable rules that more correctly represent the access that is required. Once you do that, the business justification for the access will be clear, the business owner can be assigned, and the rules can be managed throughout the rest of their life cycle.

Traffic Flow works by closely watching the access that is in use behind a single firewall rule. Then, using a complex algorithm to determine the common access paths, it recommends how you can define new access. The analysis can be as simple as showing the services used by that rule or complex rule definitions that include the source, destination and service.

Traffic Flow is available for firewall rules as well as ACLs on Cisco routers. It also has some additional uses, such as quickly helping you see what is falling through to the drop rule or creating a policy from scratch by monitoring an accept-all rule.