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

Lonnie Abelbeck lists at lonnie.abelbeck.com
Sat Jan 14 15:36:07 UTC 2023



> On Jan 14, 2023, at 8:44 AM, Buck Horn <buckhorn at weibsvolk.org> wrote:
> 
> 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

Nicely described, Buck.

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.

The GUA prefix can change and the NPTv6 adapts.

Works well for me.

Lonnie





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