Sonicwall NSA 240 Multiple WAN IP Addresses

You will need to do a few things:

1. Create an address object on the WAN zone for the the public IP address you mentioned.

2. Create an address object on the LAN zone using the IP address of the host you wish to forward traffic to on the inside.

3. Create a NAT policy that uses an original source of ANY. Select the address object on the WAN zone you just created as the original destination. Set the translated source to ORIGINAL, and the translated destination as the address object you created on the LAN side. The Inbound interface should be X1 (WAN), the outbound interface can be ANY. You can optionally choose just the port/service you want to forward, or send them all.

   You may also want to to create a NAT policy in the opposite direction to perform source translation. To do so, while initially creating the policy, check the box "create reflexive policy". This effectively creates a one-to-one NAT mapping from outside to inside for the selected hosts/IPs.

4. Create a firewall rule from zone WAN to LAN. Source address ANY, destination address should be the WAN address object created earlier. Choose the proper services.

What you want is called a NAT. (Network Address Translation, translating a publicly reachable IP to a non-routed one, or vice-versa).

For your appliance, this is the manual, and they have an example of setting a NAT in Section 4, Deployment Scenarios, which starts on page 17.