Re: [Snac] Host Requirements for SNAC Use?

[Erik Auerswald <[e-mail]>]

Hi,

On Fri, Aug 25, 2023 at 07:42:24PM +0200, Erik Auerswald wrote:
> On Fri, Aug 25, 2023 at 03:33:17PM +0000, Esko Dijk wrote:
> > [...]
> > By the way, is there any potential issue that the stub-router-provided
> > ULA prefix would somehow interfere with IPv4 connectivity? I'm assuming
> > here that IPv4 provides a default route (e.g. via the home router/ISP)
> > while the stub router does not provide a default route.
> 
> That was the case in the past, but RFC 6724 introduced a "label" for ULA
> that is distinct from GUA.  Since matching labels are preferred, the match
> between two IPv4 addresses (one label for IPv4) is preferred over the
> mismatched labels of GUA and ULA.  There is another possible failure case,
> when a remote ULA is received via DNS although the traffic would have to
> go via Internet.  This case is solved in RFC 6724 by specifying a lower
> "precedence" for ULA than for IPv4.  (Not all hosts implement the latter
> part, e.g., GNU/Linux has a higher preference for ULA than for IPv4.)

The combination of Router Lifetime = 0 with an on-link ULA prefix with a
lifetime > 0 might do the trick here, i.e., an RFC 4191 type A or B host
might ignore the stub router and thus might treat all IPv6 destination
addresses outside of that subnet as unusable.  A type C host should use
the stub router to reach the stub network.

Best regards,
Erik