F5 GTM – DNS Query Processing Order

When a DNS query arrives at a F5 GTM/DNS, this is the processing order for the DNS query.

1 – DNS Query is processed by the Listener.

2- If Recursion Desired (RD) flag is set in the incoming query and if the DNS Profile associated with the Listener has “Process Recursion Desired” enabled, the following is done:

a. DNS iRule

b. DNSSEC Key Processing

c. DNS Express

d. DNS Profiles

3 – If Recursion Desired (RD) flag is set in the incoming query and if the DNS Profile associated with the Listener has “Process Recursion Desired” disabled, the query is considered “Un-handled” and dispatched according to “Unhanded Query Action” set in DNS Profile.

4 – DNS Cache is used to handle any DNS query that doesn’t match Big-IP GTM/DNS or DNS Express Records.

Reference: K14510