Hi.  There's a tool called Firewalk which may be worth checking out, and there's a tool which looks like it's designed to audit Cisco firewalls/routers called Router Audit Tool; see http://www.cisecurity.org/bench_cisco.html

These sytems are called SEM, SIM, or SIEM (Security [Event] [Incident] Management) systems that will correlate, monitor and alert on logs. This type of system will take logs and parse it for you and make drilling into (or detecting) and issue much easier. There is no realistic way you can monitor your the tremendous amount of log data without something to help you out.