Modifying GTM DNS response based on source IP - use translation field in virtual server definition

As Hamish relates in this post:

https://devcentral.f5.com/questions/gtm-private-ip-versus-public-ip-in-gtm-dns-answers

"The translation address is NOT actually for the GTM to resolve addresses to. It's actually the IP address the GTM will 'see' the remote VS as when/if it's NAT'ed between the GTM and the LTM."

To that end, since translation address isn't really an option, you have a few alternatives. The first of course is Hamish's iRule/data group solution. A second alternative is perhaps the following:

1. Under the respective LTM server object, create your virtual server instances manually and create TWO for each WIP. For the example iRule below, I've created virtual servers with the "_ext" and "_int" extension. Example:

   test_vs_int
   test-vs_ext
   

2. Add both virtual server instances to the pool.

3. Create an address-based data group that defines your internal address space.

4. Apply an iRule like the following:

   when DNS_REQUEST {
       set server [lindex [lindex [members -list [LB::server pool]] 0] 1]
       set vs [string map {"_ext" "" "_int" ""} [lindex [lindex [members -list [LB::server pool]] 0] 2]]
   
       if { [class match [IP::client_addr] equals private_net_test] } {
           pool test_pool member "$server ${vs}_int"
       } else {
           pool test_pool member "$server ${vs}_ext"
       }
   }
   

The output of [members -list [LB::server pool]] will be a list of lists. Example:

{/Common/test_pool /Common/ltm1 test_vs_ext} {/Common/test_pool /Common/ltm1 test_vs_int}

I need the LTM server object name (ie. "/Common/ltm1"), and a virtual server name without the "_ext" or "_int" extension (ie. "test_vs"). Then, if the client is coming from the defined internal network, I'll attach the "$server ${vs}_int" pool member, otherwise the "$server ${vs}_ext" pool member.

Admittedly this option doesn't account for availability, but it is perhaps a place to start.