We configured two manual NATs for one web servers, with one NAT rules is applied for each ISP's public IP.
ISP-1 (WAN) > 10.10.10.100 to 172.16.10.100
ISP-2 (DMZ) > 20.20.20.100 to 172.16.10.100
The primary link is through ISP-1, with Priority 1.
The secondary link is through ISP-2, with Priority 100.
Therefore, the default route preference is set to use ISP-01.
Issue:
When accessing IP address 10.10.10.100, the connection works without any issues.
However, when accessing 20.20.20.100, the connection fails. After capturing and analyzing the traffic, I found that the firewall is responding to packets through ISP-1 (according to the default route) instead of the incoming interface.
Question:
Is this behavior normal, or is it possible for the firewall to respond to packets through the same interface they arrived on?