You can use BIG-IP Global Traffic Manager (GTM) as a traffic screener in front of an existing DNS server. With this setup, all DNS traffic flows through BIG-IP GTM. Listeners that you configure on BIG-IP GTM verify incoming DNS queries. If the query is for a wide IP, BIG-IP GTM resolves the request. If the query is for a destination that does not match a wide IP or for an IP address that is not configured on BIG-IP GTM, the system forwards the query to the specified DNS server for resolution. When forwarding a query, BIG-IP GTM transforms the source address to a self IP address on BIG-IP GTM.
A listener is a specialized virtual server that uses port 53 and to which you assign a specific IP address. When traffic is sent to that IP address, the listener alerts BIG-IP GTM and the system either handles the traffic locally or forwards the traffic to the appropriate resource.
You control how BIG-IP GTM responds to network traffic on a per-listener basis. The number of listeners you create depends on your network configuration and the destinations to which you want to send specific DNS requests. For example, a single BIG-IP GTM can be the primary authoritative server for one domain, while forwarding other DNS requests to a different DNS server. Regardless of how many listeners you configure, BIG-IP GTM always manages and responds to requests for the wide IPs that you have configured on the system.
A wildcard listener is a special listener that is assigned an IP address of 0.0.0.0 and the DNS query port (port 53). When you want BIG-IP GTM to handle all DNS traffic coming into your network, regardless of the destination IP address of the given DNS request, you create a wildcard listener. BIG-IP GTM responds not only to wide IP requests, but also forwards other DNS requests to other DNS servers.
Perform these tasks to send traffic through BIG-IP GTM.
Create a listener that alerts the BIG-IP system to traffic destined for a DNS server.
You now have an implementation in which BIG-IP GTM receives all DNS queries. If the query is for a wide IP, BIG-IP GTM load balances the request to the appropriate resource. If the query is for an IP address of a DNS server, BIG-IP GTM either routes or forwards the query to the DNS server for resolution.