[address-policy-wg] IXP pool lower boundary of assignments

* Wolfgang Tremmel

> > No. But renumbering an IX is *pain*. A lot of pain. You want to
> > avoid that if possible.
> > A /26 allows (given that the IX uses about 2-4 IPs itself) about 60
> > customers.
> > 
> > So according to the numbers, for 70% of the IXes this will never
> > fill up, so no need for renumbering.
> > Depending on how quickly it filled up, you then go either for a /25
> > or a /24.
> > 
> > To sum up:
> > - if you start with a /26 ==> 30% has to renumber
> > - if you start with a /29 ==> 75% has to renumber ---> more pain!

I do not think that insulating IX-es from possibly having to renumber
when they double in size should be something this policy should aim to
accomplish. (If it was, we could simply give everyone /22s or larger.)

IPv4 is a limited and finite resource – the goal should be to make it
last. Looking at Matthias's graphs, for each new IX that is assigned a
/26, there is an about 70% chance of that assignment being wastefully
large.

Making such assignments will inevitably result in other new IX-es being
denied assignments, because there is nothing left, because the space
those IX-es *could* have used was given to first IX – even though the
first IX had no need for it.

So, all in all, I think that assigning IX-es the amount of space they
*actually* need, but no more, and require them to renumber into a
larger prefix whenever they double in size is a fair deal, when
balanced against avoiding waste and preserving space for future IX-es
(and existing growing IX-es for that matter).


* David Farmer

> I think maybe we want something in between; what do /27 and /28 look
> like?
> 
> /29 could be forcing too much pain into the system, and /26
> probably isn't enough pain in the system.
> 
> Furthermore, /29 seems a little too small for a reasonable growth
> cycle before having to renumber. 50% fill of a /29 would be 3 of 6
> usable addresses. Meaning many IXes could almost immediately qualify
> for a larger subnet, and they would have very much time to implement
> a renumbering process.

The policy states that you get what you need to have a 50% utilisation
one year from assignment.

Thus, in order to get an initial /28 assignment and skip over a default
/29, the IX would need to have a realistic plan to have eight members
within a year of the founding of the IX (or possibly just six, if the
NCC considers the network and broadcast addresses as «utilised»).

That is a *very* low bar to clear.

But if IX cannot clear that low bar, I'd say they should not start out
with a /28 (or larger) either.

https://www.ripe.net/publications/docs/ripe-733#61

> Basically, a /29 is probably too small to be practical. 
> 

Well, according to Mathias's report, 25% of all IX-es would manage just
fine with a /29…

By the way, last I checked there were a number of unassigned fragments
smaller than /24 rotting away in the NCC's inventory, due to there
being no policy that allowed for their assignment. IX-es are one of the
very few places where those can be used, so they could be all added to
the reserved IXP pool and actually do some good there.

Tore