A forwarder is a server that forwards DNS queries to DNS servers that are outside the forwarder server’s network. Queries that cannot be resolved locally are forwarded to other DNS servers. A forwarder accumulates external DNS information in its cache as it resolves DNS queries. To configure the NetScaler as a forwarder, you must add an external name server (a name server other than the Citrix NetScaler appliance).
The NetScaler appliance allows you to add external name servers to which it can forward the name resolution queries that cannot be resolved locally. To configure the NetScaler appliance as a forwarder, you must add the name servers to which it should forward name resolution queries. You can specify the lookup priority to specify the name service that the NetScaler appliance must use for name resolution.