Re: [v6ops] [IPv6] draft-ietf-6man-rfc6724-update might break current ULA+IPv4 hostnames

[Ted Lemon <[e-mail]>]

I don’t know where this would actually go wrong, though. These ULAs are
only ever seen on the adjacent link. They aren’t routed. They aren’t
discoverable other than on the adjacent link. So if you can see them, you
can reach them. If you are worried about the case where snac numbers the
adjacent link because it’s v4only, that’s also no problem because there’s
no competition between a routable v6 source address and an unrouteable one.

There is the edge case where there is no prefix on the link that is
suitable for use by the snac router, but there is a prefix on link that is
routed.  In this case if the operator doesn’t configure RA guard, the
non-routable ULA address could wind up being used as a source address.
However, if the host follows rule 5.5 this won’t happen. And I think this
is a misconfiguration in any case: if you want to control addressing on a
link, I think you have to use RA guard as well as DHCP.

Op zo 12 nov 2023 om 09:37 schreef Ole Trøan <[e-mail]>

> Matk,
>
> > On 12 Nov 2023, at 12:19, Mark Smith <[e-mail]> wrote:
> >
> > Normally, Host A's ULA address should have a path through the local
> > network to Host B's ULA address and vice versa, so Host A and B's ULA
> > addresses should be preferred over Host A and Host B's GUA addresses.
>
> Come to think about it. Wouldn’t RFC6724 also fail in the MPMH case?
>
> Source host A with GUA1+GUA2 (from ISPA AND ISPB)
> And destination host B with GUA3.
>
> 6724 will return the source address with the longest matching prefix to
> GUA3. So only one of these:
>
> {GUA1, GUA3}
> {GUA2, GUA3}
>
> The SA determines exit path, so depending on which ISP is down.
> Communication will fail.
> Redundancy is the whole point of multi-homing…
>
> The other case I am concerned about is the one where within a single
> network multiple routers make up their own ULA and use that to assign
> addresses to directly connected hosts but do not participate in routing. We
> then have multiple disjointed ULA domains within the network. With RFC7078
> and SNAC routers I am not sure if we can avoid that. This would possibly
> have been cleaner with site-locals.
>
> O.
>