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 passively checks for DNS packets on port 53 and the IP address you assign to the listener. When a DNS name resolution request is sent to the IP address of the listener, BIG-IP GTM either handles the request locally or forwards the request to the appropriate resource.
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 respond to DNS name resolution requests coming into your network, regardless of the destination IP address of the given request, you use a wildcard listener.
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.