I have a site-to-site VPN set up with a vendor. Let's say the tunnel endpoints are 188.8.131.52 on my side and 184.108.40.206/24 on the vendor's side (which get's NATted to their LAN of 10.x.x.x). This is working fine, I have a SonicWall and I have a VPN policy setup so traffic to 192.1.2.x from my side goes through their VPN and reaches the correct hosts.
The problem is I have an (old, unmodifiable) application that is trying to connect to 10.0.0.10 on their network. If I can make this go through the VPN as if it were 220.127.116.11, then it would reach the correct destination. The vendor is unwilling to add 10.0.0.10 as a tunnel endpoint.
I tried a NAT policy to transform traffic towards 10.0.0.10 to 18.104.22.168, but I believe that doesn't also send it through the VPN because NAT is applied to traffic as it leaves the firewall and after the point where it would have triggered the VPN routing rule. Basically I want to take any traffic to 10.0.0.10, change its destination to 22.214.171.124, and send it through the VPN tunnel for 126.96.36.199. I'm not an expert at firewall config, can someone point me in the right direction?