When the F5 BIG-IP system receives a DNS request, it first checks the type of record in the request (A, AAAA, CNAME, A6). If the request matches one of these types, the BIG-IP forwards the DNS request to the GTM module to handle it, as the GTM module is responsible for Global Traffic Management operations.
The GTM module then checks the DNS query against the available Wide-IP list of Fully Qualified Domain Names (FQDNs). If a match is found, the GTM module performs the Global Server Load Balancing (GSLB) operation to ensure efficient traffic distribution across the available resources.
If the GTM module does not find a match in the Wide-IP list, it forwards the query to a pool of DNS servers.
The GTM inspects and checks all responses coming from these DNS servers to ensure accurate and reliable DNS resolution for the client's request.
In case the GTM module finds a response from the DNS servers that contains a name matching any Wide-IP, it intercepts or postpones this response. It then applies the GTM operation on it, rewrites the response as needed, and sends it back to the client. This process ensures that the client receives the correct and optimized response for their DNS request.