Gtm to forward selective traffic to another dns server

By URL you mean FQDN domain name right ? It is not an issue to capture the DNS request with an irule attached to the DNS listener and resolve it to the Virtual server listener on the other device as I gave you the link for the DNS request event.

 

https://clouddocs.f5.com/api/irules/DNS_REQUEST.html

https://clouddocs.f5.com/api/irules/DNS__question.html

 

Example:

 

when DNS_REQUEST {
if { [DNS::question name] equals "the domain you want to redirect" } {
host 10.20.20.20
}
}

 

You can add type with the "DNS::question" command in the "if" statement to also select to send maybe just A records to the other GTM device etc.

 

 

But maybe from what I read you want the F5 DNS to delegate the DNS resolution to another F5 then read the article below how to do this on the F5 bind but the traffic is captured by a wide ip that matches a more general domain then you can try again with an irule to send the traffic to a DNS listener pool that has your DNS server and attach the iRule to the Listener object.

 

https://support.f5.com/csp/article/K34150459

 

 

when DNS_REQUEST {
if { [DNS::question name] equals "the domain you want to redirect" } {
pool <your DNS/LTM pool with the other GTM listener IP address>
}
}