Pulling my hair out to find a solution to this issue. I thought I could solve it with Nat however I cant get it working. Basically I have two internet facing IP's and I want to be able to access Exchange OWA & SMTP from either of them. However based on what router owns the HRSP IP at any given time, that is the only Public IP that will work.
I have HSRP set up with an IP SLA to detect if the public interface is down on the primary link to enable redundancy. I also have DNS failover configured with our DNS provider however as they are two separate monitoring systems it is often not robust. Example sometimes the DNS failover detects that the primary is down. Maybe its a false positive or it was just a blip, during that time staff cannot access mail as in order for this redundancy framework to work, both need to work in concert in terms of failing over.
What I want to be able to do is permanently accept traffic from both internet interfaces. I thought I could nat the public ip to ensure traffic went back to the correct border router however cant seem to get that working. I have another solution that I think can work however just want to pick brains to see if this can be simply fixed. Mt other solution is to deploy another exchange front end server and use policy routing to ensure its outbound traffic always goes via the secondary router.