Dear experts, please refer to my network diagram. I have 2 internet link from 2 different ISP. 1 is main and 1 is backup. I don’t really need WAN load balancing but I would want my mail traffic to come in from either link all the time through primary and secondary MX records. NAT is configured in both the ASA. I can have all my outgoing traffic going out through a single link no problem.
I’m trying to add in the 1902 router. In my router, I have a statement ip route 0.0.0.0 0.0.0.0 192.168.120.1. This will force all outgoing traffic out via the 1st link. If the 1st link is down I must logon to the router and change the gateway to the other link 192.168.120.2 (Singnet). Can I have more than 1 default gateway so that if I link is down it will route to the other link?
If I only configure 1 default gateway in the router, traffic only comes in from outside to inside through NAT from the active link. That means if my default route points to the ISP A, mail traffic comes in via ISP A and not B. How can I achieve mail to come in from either link all the time without adjusting the default gateway in the router?