I've just added a new/second ISP line to my gateway and made this my primary ISP line. ISP Redundancy is configured.
LAN traffic to the Internet leaves via the default gateway of ISP line 1 - the new line. All good.
I still have a load of servers with static NAT on what is now the secondary ISP line. These no longer work. Tcpdump shows traffic arriving from the Internet via ISP line 2, but return traffic routes out via the default gateway on ISP 1. Asymmetric routing...
How do I get this traffic to return via the interface it arrived on - back via ISP 2?
I've got other gateways with the same dual ISP configuration, and they work fine. Return traffic goes back out via the interface from which it arrived. But not this gateway. Any ideas why not and how to fix it?
