Provide custom resolution based on Source and URL

I'm assuming when you say URL, you actually mean the domain name.

When you reference classes, those are BIG-IP Datagroups, so in the LTM section, go to iRules and then datagroups. Add one of type address for IP_Data_Group and one of type string for the FQDN's you want to match against.

Then I think the rest would be something like this

when DNS_REQUEST {

  log local0. "client ip is [IP::client_addr] and domain name requested is [DNS::question name]"

  if {[class match [IP::client_addr] equals IP_Data_Group] and [class match [DNS::question name] equals FQDN_Group] } {

    log local0. "matched, going to pool1"

    pool pool1 

    }

    else { 

      log local0. "no match, going to default pool2"

      return

      }

}