We have one router with connections to two different ISPs. Static NATs are configured to servers using IPs from ISP A. The customer is migrating everything eventually to ISP B. At this moment, we want to make all outbound traffic flow through ISP B but keep the static NATs to the servers on ISP A.
default route - ISP B
server 1 static NAT ISP A
server 2 static NAT ISP A
server 3 static NAT ISP A
The problem is that once ISP B is the default route, the static NATs break. How do we get traffic meant for the servers that comes in ISP A to return through ISP A?