@Hydros 

Hey!

If I'm not guess mistaken, you want to set up two VPNs on both ER605s at the same time, one of them as a backup?
I don't think it will work because you are setting up two VPNs with the same WAN IP, LAN IP on both ends, so it is actually enough to set up one successfully, because as far as I know the VPN channel will automatically detect a reconnection if it is disconnected.

And setting up a VPN on the W9960-W9980 probably won't work either, because the data exit at both ends is still the ER605 on the front end, same reasoning as above, in my opinion.

@Hydros 

If you enable DPD, it will automatically detect disconnection and reconnection.

Hydros wrote

 

And what about this solution:

I create multiple Vlans at both ends. Then setup VPN tunnels between them. For example at one side I create 192.168.1.0 and 192.168.2.0 and on the other side 192.168.10.0 and 192.168.20.0. Then tunnel will be 192.168.1.0==192.168.10.0 and 192.168.2.0==192.168.20.0 . Then I assign 2 IP adresess to my PCs at both ends. ...Do you think it will work ? 

Thanks 

In fact, to be honest, I think it is also meaningless, because when one of the disconnected (such as 192.168.1.0 == 192.168.10.0 disconnected), then the two ends of the device in this LAN is still no way to communicate, only 192.168.2.0 == 192.168.20.0 this section of the two LAN devices can still communicate normally but already, then this case is not what you call VPN backup.

I think that DPD is very useful for you. It's got the similar features you're looking for.