I'm trying to figure out how to implement DMVPN in two regions with two hubs in each regions, one as primary and the other as backup. Please see attached diagram for clarity.
My setup is two regions; each region has a primary hub and a secondary. Each spoke has two tunnel one for their respective region's hub and one to the other region's hub. The backup path is controlled using added delay on the tunnel interface to increase EIGRP metric for routes learn. There are two DMVPN networks blue and green.
What I would like to do it use the secondary hub in each region, but without creating another tunnel.
I'm using Phase 3 DMVPN (summary routes and nhrp redirect).
Does anyone have any suggestion how to implement it? If I just add the Hub 2 to each network using the
'ip nhrp map (hub2ip tunnel) (hub2 ip ext)'
'ip nhrp nhs (hub2)'
.. how would it know which nhs to use since? Would it just use both of them? Is there a metric to control that? (I know you can control it by which dest subnet should use which nhs (i.e: ip nhrp nhs (hub2) 10.0.0.0/9 and ip nhrp nhs (hub2) 10.128.0.0/9) to load balance it, but i'm trying to setup it up as a failover backup and not to load balance).
Any ideas or suggestions would be greatly appreciated.