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

[David Farmer <[e-mail]>]

Ole,

On Sun, Nov 12, 2023 at 8:37 AM Ole Trøan <otroan=
[e-mail]> wrote:

> 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?
>

Yes, it will fail in some cases but succeed in others.


> 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…
>

If there is a soft failure of the provider of the selected SA, there will
be a failure. If there is a hard enough failure to cause the withdrawal of
one of the RAs, then redundancy will work.


> 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.
>

In many cases you refer to, the disjoint ULA domains are likely to be
ULA-only domains. If there are ULA-only domains, there will only be ULA
destinations to try, and they will be reachable or not. When we mix ULA,
GUA, and IPv4, things get really complicated. ULA-only domains should be
relatively straightforward.

Thanks

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