Using Network Address Translation (NAT) Dispatcher capability removes the limitation for the backend servers to be located on a locally attached network. When you want to have servers located at remote locations, you can use the NAT technique, rather than using a Generic Routing Encapsulation (GRE)/Wide Area Network (WAN) technique. With the NAT forwarding method, Dispatcher load balances the incoming request to the server. The server returns the response to Dispatcher. The Dispatcher machine then returns the response to the client.
You will need three IP addresses for the Dispatcher machine – NFA, cluster, and return address. The return address is a unique address or host name that you configure on the Dispatcher machine. Dispatcher uses the return address as its source address when load balancing the client's request to the server. Using the return address ensures that the server returns the packet to the Dispatcher machine rather than sending the packet directly to the client (Dispatcher will then forward the IP packet to the client).
You must specify the return address value when adding the server. You cannot modify the return address unless you remove the server and then add it again. The return address cannot be the same as the cluster, server, or NFA address. When you use the NAT forwarding method, you must define a return address for communication between Load Balancer and the backend servers. The number of connections that Load Balancer can keep active with the backend server is limited by the number of return addresses that are defined. Load Balancer uses ports that are based upon the return address only; not the return address and server combination. When all the available ports are in use, additional connections fail. In a busy environment, use multiple return addresses to prevent a shortage of available ports.
In addition, while configuring NAT, you also need to specify the router address, for example, the address of the router to the remote server. If this is a locally attached server, enter the server address, unless the server is located on the same machine as Load Balancer. In that case, continue to use the real router address.