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

[Buck Horn]

On 14.01.2023 12:40:18, Chris Webb wrote:

>If we are advertising local (ULA) prefixes but no globally-routeable
>prefixes, we should similarly not configure clients with a default route.
>Set the router lifetime to zero in this case too.

I disagree here.

While ULAs are not routable on the global Internet, they can be used 
within private scopes, like a same-site network with multiple 
routers/segments, or even spanning multiple geographically distributed 
networks within the same organisation.
This is one of the design goals of ULA, avoiding some of the drawbacks 
of the previous attempt of IPv6 site-local addresses (deprecated 
fec0::/10).

Quoting from RFC4193 'Unique Local IPv6 Unicast Addresses':

 >  This document defines an IPv6 unicast address format that is globally
 >  unique and is intended for local communications [IPV6]. These
 >  addresses are called Unique Local IPv6 Unicast Addresses and are
 >  abbreviated in this document as Local IPv6 addresses.  They are not
 >  expected to be routable on the global Internet.  They are routable
 >  inside of a more limited area such as a site.  They may also be
 >  routed between a limited set of sites.

and further down:

 > In practice, applications may treat these addresses like global scoped 
addresses.

Wouldn't it thus seem more sensible to keep advertising a non-zero 
router lifetime along with a ULA prefix for a dnsmasq instance running 
on a router?

Kind regards,
     Buck