Re: Network merge [Re: RFC6724-bis?]

[David Farmer <[e-mail]>]

On Sat, Sep 24, 2022 at 15:38 Brian E Carpenter <[e-mail]>
wrote:

> Just focusing on the corner case:
>
> On 25-Sep-22 07:47, Nick Buraglio wrote:
> >
> >
> > On Fri, Sep 23, 2022 at 8:12 PM Brian E Carpenter <
> [e-mail] <mailto:[e-mail]>> wrote:
>
> ...
> >     But there is still a corner case: if two networks using ULAs are
> >     merged, and the necessary routes are installed, the individual
> >     hosts would still need manual intervention. A high precedence for
> >     fc00::/7 would avoid that.
> >
> >
> > At least to me at this time it seems that although this use case is
> real, it should just be noted as an edge case that is out of scope.
>
> I think we need to say a little more, since the network merge case was one
> of the original motivations for ULAs in the first place (otherwise,
> statistical uniqueness has no real value).
>
> At least, we need to say that in the case of a network merge, human
> intervention to configure ULA precedence will be needed. I still find that
> unsatisfactory, since the idea was always that unplanned merges might
> happen (in unmanaged networks, not in enterprise networks). If we decide to
> leave that unsolved, I think we'll be back to this problem later.
>
> Now as to how to fix this without a global precedence for ULAs, I am
> wondering about a PIO with L=0 and A=0 (exactly as recommended in RFC 8028,
> but for other reasons). If a host sees such a PIO for a ULA prefix, it
> could serve as a signal that the prefix is to be given a suitable
> precedence, even though it is not on-link and not used for SLAAC.
>
> (Credit where credit is due: Ted Lemon suggested this.)


I’ve been thinking that either a PIO or a RIO from within fc00::/7 should
trigger an entry in the table. If the prefix in the PIO or RIO is longer
than /48, the covering /48 should be added to the table. Otherwise, if the
prefix is /48 or shorter the prefix should be added to the table as-is. In
most case unless a PIO is a /64 it will likely have L=0 and A=0.

While probably not recommended, it would be possible for a network operator
to signal the entire ULA range as being local, using a PIO for fc00::/7
with L=0 and A=0, for example.

Finally, there should probably be a short discussion of managing the table,
such as removing an entry when the PIO is no longer valid and similarly for
a RIO.

Thanks
-- 
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David Farmer               Email:[e-mail]
Networking & Telecommunication Services
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