How to forward one IP address to external IP.

Question

I am migrating servers from one ISP to another. 
 The old ISP has a Sophos UTM 9 where I have root access. (But the ISP has no knowledge of Sophos) 
 There is incoming traffic to the old server on a IP address I cannot change. No DNS is used. 
 I need to forward IP traffic from this old IP to the public IP of the new server (by another ISP). 
 The new server has just one public IP. I have no access to any router by the new ISP. 
 
 On a CISCO firewall you would do like this: 
 nat (any,outside) source dynamic any oldIP destination static oldIP newIP

Jaydeep · Accepted Answer

Hi Johan Franson 
 This is possible. Given that your Sophos UTM 9 has routes available to the Public IP of the new server. You should create a FullNAT (DNAT will work only if the new server's traffic is routed via Sophos UTM9). So here you go: 
 
 This should help you forward the traffic to your new ISP IP address without any modification on the new router. There will be an issue where your servers won't be able to see the original IP address of the request but that's the trade-off you will have to make if new server's traffic is not routed via Sophos UTM9. If it does, you can do a DNAT and that should work as well.