Okay so you are not proposing a backup router,
but a backup such that at least one ISP is available at all times on the LAN, if one goes down.
Well you dont need two routers for that, one will suffice!
It all depends on how you setup your routing for the most part.
Attach both ISP modems to the primary router (use the second hapac as a switch/AP for example).
What would a more interesting exercise is how to have a backup router in case the primary router fails (assume dead dead dead)
Thus you would need a managed switch (even just basic port translation)
such that both ISP connections go into the switch (lets say port1 and port2, Port1 is connected to ports 3,4 and Port 2 is connected to ports 5,6
Thus hapac one is connected to switch ports 3 and 5
Thus hapac two is connected to switch ports 4 and 6.
That way both routers have access to both ISPs full time.
Then you will need one connection dedicated I think, between the two routers.
The functionality in the router that applies is VRRP.
I'd rather manage rats than software. Follow my advice at your own risk! (Sob & mkx forced me to write that!)
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