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.
Lets say that you have domain.com hosted with a 3rd party DNS provider and you would like to create GTM (BigIP-DNS) DNS load balancing by utilizing Sub-Domain Delegation.
In this scenario, there are 2 GTM. One in each DC (DC-1 & DC-2). The basic set up has been completed and the GTMs are in a common sync-group.
Create A-Records for the 2 GTM using their Listener IP addresses:
gtm1.wip.domain.com. IN A 100.100.100.100
gtm2.wip.domain.com. IN A 220.127.116.11
gtm1 and gtm2 exist in DC-1 and DC-2 respectively and 100.100.100.100 & 18.104.22.168 are the listener IP address configured on gtm1 and gtm2.
Delegate the sub-domain to the GTM using NS Records:
wip.domain.com. IN NS gtm1.wip.domain.com.
wip.domain.com. IN NS gtm2.wip.domain.com.
Use CNAME records:
www.domain.com. IN CNAME www.wip.domain.com.
The above DNS records (A, NS & CNAME) will be added to the 3rd party DNS records that is hosting domain.com. Any request for
will be sent to the 3rd party DNS provider which will then resolve to
because of the CNAME and that will be handled by the GTMs because of the NS & A records.
SOL277 – Sub-domain delegation.