[Dnsmasq-discuss] [PATCH] Don't advertise a default v6 route with no routeable prefixes

[David Kerr]

To reinforce Lonnie's point.  One reason that ULAs and NPTv6 is so useful
is that it makes for easier internet failover.  I have a Comcast/Xfinity
main connection and a T-Mobile 5G backup/failover.  If I failover from
Comcast to T-Mobile then the GUA prefix assigned to me by Comcast is not
going to work over T-Mobile.  But NPTv6 will map to the correct GUA prefix
for the internet connection being used.

If I want to access services inside my network from outside then I can
configure a VLAN that does use [the comcast] GUA delegated prefix and
connect those few devices that do need to be accessed from outside to it.

Also, if a client device attempts to talk IPv6 to an external host and it
fails (in your example because the router has no GUA prefix to map to),
then I suspect that a client will fallback to IPv4.  There may be
some initial delay, but it should still work.

David

On Sat, Jan 14, 2023 at 12:05 PM Chris Webb <chris at arachsys.com> wrote:

> Lonnie Abelbeck <lists at lonnie.abelbeck.com> wrote:
>
> > For years I have used only ULAs for local networks (and VPNs) and at
> the
> > edge enable Network Prefix Translation (NPTv6) to assign static local
> > routable IPv6 subnets to have their prefix mapped 1:1 to Global Unicast
> > Addresses (GUA) for global Internet access.
>
> Interesting. I agree this setup wants a default route despite being
> entirely ULA, and therefore argues against unconditionally zeroing the
> lifetime.
>
> Conversely, with the current behaviour, a router that has no v6
> connectivity but wants to provide a ULA prefix locally will incorrectly
> configure clients with an invalid v6 default route.
>
> Looks like a general solution needs explicit configuration rather than an
> unconditional behaviour change like I'm able to use locally.
>
> Best wishes,
>
> Chris.
>
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