Using IPv6 and ULA for greater resilience

[Daniel Pocock <daniel@pocock.pro>]

For a home network or a small office, what is the best practice for
using ULA in parallel with the prefix from an ISP?

Consider the following:

- router (OpenWRT or Debian) receives prefix delegation from ISP and
shares it, and also a ULA prefix, over the LAN with DHCPv6

- there is a small server or NAS running Debian on the LAN

- the router is also the local DNS and it is synchronized with the
DHCPv6 leases (e.g. the default OpenWRT odhcpd/dnsmasq setup)

- the aim is that if either the router or server stop working,
everything else (e.g. local DNS, communication between other local
machines) keeps working using the ULA prefix.  Example: if the router
stops working, the local workstations need to be able to resolve the
hostname of the server and contact it using the ULA addresses.


Looking around online, I've found various suggestions but nothing that
appears to be a complete and concise solution.  For example, one blog
suggested using two ULA prefixes, one for devices with static addresses
(the server) and another for devices with dynamic addresses (e.g.
workstations, laptops).  It appeared a bit overcomplicated and didn't
cover the DNS.

An easy solution might involve putting static addresses on everything
and putting the server's ULA address in every hosts file but it would be
nice to find a solution that is entirely dynamic with only the router
and server having any static configuration entries.

Which solution would be suggested for synchronizing the DHCPv6 leases
and DNS entries between both router and server?  OpenWRT ships odhcpd
and dnsmasq, Debian has the ISC equivalents as well.  Which solutions
are people using?

Regards,

Daniel