Exchange with two ISP on F5 DNS

Hi Guys, I have LTM, GTM and two ISP lines ISP-A and ISP-B. If ISP-A goes down, mail traffic should failover the ISP-B. My Config;

 

ISP-A --> 1.1.1.1

 

ISP-B --> 2.2.2.2

 

Exchange Virtual Server --> 10.10.66.66

 

FW NAT --> 1.1.1.1 --> HTTP/HTTPS --> 10.10.66.66

 

GTM Record --> mail.test.com 1.1.1.1

 

internal DNS --> mail.test.com 10.10.66.66

 

I want to add second ISP for redundancy. what do i need for that?

 

My plan is that;

 

Creating second NAT which is; 2.2.2.2 --> HTTP/HTTPS --> 10.10.66.66

 

Creating Second A and MX record on GTM --> mail.test.com 2.2.2.2

 

How can I check ISP links whether they are up or down.