How to utilize a spare ISP Link at each DC for redundancy?
Our current config is as follows. We have 2 data centres, each DC contains one GTM and one LTM. The setup works really well so we are covered for the following scenarios.
One GTM fails
One LTM fails
One ISP Link fails.
What we have available is a spare ISP link which is owned by a subsidury company. What I would like to do is to utilize the secondary ISP links for redundany purposes on the small chance we lost both our primary ISP links (one at each DC).
For each domain we host our GTMs contain one Wide-IP and one Pool. The pool contains two members, one from each data centre using the public ip of our primary ISP. What I believe I could do is create secondary pools and create members using the public ips available from our secondary ISP. I could use Global Availability as the load balancing method on the Wide-IP to ensure the pool associated with the primary ISP is always used unless it becomes unvailable.
Having thought about this there appears to be a couple of challenges.
Each GTM has one dns listener which is an ip address from our primary ISP. If we lost both primary ISP links at both sites the dns listeners won't be available. It seems I need to create additonal listeners from the secondary ISP Link.
Would I therefore need to create additional name servers for each domain which use the IP from the secondary ISP link?
The other problem is the default route which the GTMs use. This points to the upstream router of our primary ISP link. If we lost our primary ISP links at both DC's how could we automatically failover the default route on the GTMs to use the secondary ISP Link? I know I could possibly use a default gateway pool but I'm not sure how this would allow me to monitor the connection upstream of our ISP router?
Just wondered if anyone else has configured anything like this?