Subj : Two ISPs and backup for a home network (dual-homing)
To   : Victor Sudakov
From : Alexey Vissarionov
Date : Wed Jun 30 2021 05:24:00

Good ${greeting_time}, Victor!

29 Jun 2021 21:43:24, you wrote to me:

 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?
 AV>> This is the preferred mode of operation, but it has (only) two
 AV>> disadvantages: 1. All hosts in the LAN must be able to do the
 AV>> switching|balancing on thy own (that means, run Linux; the
 AV>> BSD-style networking stack, like the one used in Windoze, has
 AV>> very limited functionality). 2. This may require some manual
 AV>> configuration on every of them. Not really a problem, but may
 AV>> be boring.
 VS> This is not feasible because most of those LAN hosts are smartphones,
 VS> smart TVs, vacuum cleaners, cameras and other IoT devices.

Most of these devices have Linux kernel, but crippled userspace.

 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
 VS>>> always the same. Can anyone enlighten me?
 AV>> This is second option, but you'd lose the main advantage of IPv6:
 AV>> the use of publicly routed addresses.
 VS> Indeed. I don't like the idea of using NAT in IPv6 even if I could.
 VS> So what's the solution?

For dumb devices, especially portable, I'd suggest using NPT. Fully functional computers may be connected to some other VLANs (two at once in your case) and configured to use real addresses.


--
Alexey V. Vissarionov aka Gremlin from Kremlin
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