Hello there,
I’ve got two offices and these are connected via GRE IPSec + OSPF. Both have failover channels + script which controls switching to failover and back to main.
Everything works fine until Failover comes in. Connections interruptions are quite common.
So I want some kind of redundant GRE-tunnel, but which will be up only if failover switch will be performed. Is there some kind of easy way to achieve this?
GRE + Bonding “active/backup” failover?
I am afraid that if you already have OSPF up and running, it is the easiest way to handle failover, I'm just suprised you need scripts in addition to it.
Is NAT in use on the routers? It can be the cause of problems when one of the WANs goes down.
When talking about activating the backup tunnel only when the primary one goes down, are you concerned about keepalive traffic or there is another motivation?
Bonding only works with L2 interfaces, so you can bond together EoIP ("ethernet over GRE") tunnels but not "GRE" ("IP over GRE") ones.
Oh… 
yes… too many EoIP used 
Is NAT in use on the routers? It can be the cause of problems when one of the WANs goes down.
Yep. LAN on both ends are beyond NAT.
When talking about activating the backup tunnel only when the primary one goes down, are you concerned about keepalive traffic or there is another motivation?
There are some resource that LAN2 uses from LAN1.
When I tried to duplicate tunnels, nothing worked for me when changing the address, namely, the backup tunnel did not rise. Today I will try again to conduct a small experiment and I will write according to the results.