[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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