*** Overview of DNS Query Processing on F5 BIG-IP Systems ***

* If the "Recursion Desired (RD) Flag = Set" in the request header, and the "Process Recursion Desired = Enabled" in the DNS profile:

 1- DNS iRules
 2- DNSSEC Zone Processing
 3- Wide-IP Processing (GSLB)
 4- DNS-EXPRESS Zone Processing
 5- DNS-CACHE (Local-Zone / RPZ / Forward-Zone)
 
 * Then, the "Unhandled Query Actions" setting controls how the system handles packets that do not match the previous steps...
 
 * If the "Recursion Desired (RD) Flag = Set" in the request header, but the "Process Recursion Desired = Disabled" in the DNS profile:

 1- The request is immediately considered "Un-handled", and dispatched according to the "Unhandled Query Action" setting in the DNS profile.
 2- If the "Unhandled Query Actions = Allow", then:
 2-1- DNS-CACHE (CACHE / Load-balancing)
 2-2- Local-BIND
 2-3- Drop