Hello, i have a 2865ax and i'd like to setup automatic failover to another modem/router
I'd reading online that for this to happen automatically it would need to be the same router, like a 2865lac for example
Is that correct? 
Or could i buy an older cheaper version like 2860la and still be able to configure automatic failover?

thank you
zac
 

Are you after a WAN failover (when one WAN connection dies - another one to kick in) or are you after a router failover (when one router dies and another is meant to kick in) ?

ahh yes good point. i should have said i'm looking for WAN failover
thank you
zac

In which case you don't neccessarily need another router then - just connect both services to the one router...

This is the whole point of having a router with multiple WANs
So you can have, for example,e ADSL/VDSL on WAN1 and then, for example, an FTTP on WAN2
Both will be live, both can be set up to be 'load balancing' the traffic or chosen WANx can be set to be a primary source of the internet, and then another WAN to become a 'failover' one.
All done via one router/device.

yes I get your point. My situation is:

I'd like my redundant WAN to be a 4g sim card connection. However the reception in my area is not great so a usb dongle in my 2865ax router wont do it.

So I had planned to buy an external LTE antenna and buy a second vigor with LTE antenna connections on the back that I can hook up to my external antenna.

Hope that makes sense.
thank you
zac