Good ${greeting_time}, Victor!

28 Jun 2021 21:07:18, you wrote to All:

 VS> What if I had two IPv6-capable ISPs for my home, and a /64 or a /56
 VS> from each of them? Is it possible to setup a backup link this way?

Yes.

 VS> I know that my home router can advertise multiple global IPv6
 VS> prefixes into the LAN, but how will LAN hosts failover to the
 VS> backup gateway if the primary ISP fails? They will have IPv6
 VS> addresses from both blocks, which should they choose for their
 VS> outgoing src address?

This is the preferred mode of operation, but it has (only) two disadvantages:
1. All hosts in the LAN must be able to do the switching|balancing on thy own (that means, run Linux; the BSD-style networking stack, like the one used in Windoze, has very limited functionality).
2. This may require some manual configuration on every of them. Not really a problem, but may be boring.

 VS> With two IPv4 ISPs and NAT, the setup is rather trivial, outgoing
 VS> connections will work via either of the ISPs because the hosts
 VS> needn't be aware of the failure, and their src private IP is always
 VS> the same. Can anyone enlighten me?

This is second option, but you'd lose the main advantage of IPv6: the use of publicly routed addresses.


--
Alexey V. Vissarionov aka Gremlin from Kremlin
gremlin.ru!gremlin; +vii-cmiii-ccxxix-lxxix-xlii

... god@universe:~ # cvs up && make world
--- /bin/vi