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

* Marcus Stoegbauer

> In the case of IXPs I consider larger assignments up to a certain
> point as a technical necessity rather than a situation we need to
> rectify. Handing out /29s to a new IXP IMO puts a large burden on
> newly founded IXPs (since they would need to renumber earlier) which
> gives them an unfair disadvantage. This I consider a larger problem
> than eventually running out of addresses in the pool altogether.

That's a fair position to have, and if it is indeed now the desire of
the IXP community to continue overassigning to IX-es founded in the
near future at the cost of not being able to assign anything to IX-es
in the further future, then by all means, be my guest.

I do note that this does seem somewhat at odds with the stated
rationales of proposals 2011-05 and 2019-05, though.

> My counter argument is twofold:
> 
> One, it's easier for an IXP to grow from 4 to 8 members than it is to
> grow from 40 to 80 members, so the likelihood that a very small IXP
> would need to renumber is larger than for already established IXPs
> with larger address space.

Perhaps so, but do keep in mind that an IX that are expected to grow
past 5 members within one year of its founding would not get a /29 to
begin with, they would start out with an initial /28 (or bigger).

> Two, the numbers Matthias supplied are great and we can definitely
> get some information for this discussion from them. However, they are
> a snapshot in time. For the argument you are making we would need
> this data over time, and the question to ask would be "How long does
> an IXP which fits in a /29 stays in this category?". We cannot get
> this information from the data, so we shouldn't base assumptions and
> policy on this.

That is a valid point, and it would indeed be useful to know for how
long, on average, an IX stays within a given bracket.

However, both the current snapshot and the one back in 2019 showed that
small IX-es are overrepresented, with the very smallest («would fit
into a /29 with 100% overprovisioning») being the most populous bracket
by a wide margin. I can think of only two explanations for this:

One being that many small IX-es simply do not grow, or at least are
growing very slowly, thus staying for a long time within a bracket.

The other one is that the rate of new IX-es being founded is
accelerating, in other words that the rate of new small IX-es showing
up is exceed the rate of recently founded IX-es growing out of their
initial brackets.

Either way it seems like continuing a policy of overprovisioning would
hasten the total exhaustion of the IX pool, which of course is to the
detriment of any new IX-es appearing past that point in time.

Matthias's report makes the following observation: «the default policy
of assigning /24s has created large amounts of unused space», which is
100% true. I warned against exactly this against during the discussion
of 2019-05, but nobody listened, and so here we are again. Anyway,
dealing with this now by adjusting down the minimum assignment size to,
say, /26 will not solve this fundamental issue that Matthias observed,
we will still be overassigning space, just at a reduced rate.

I predict that that if we go for a /26 this time, a few years from now
we will end up in the exact same spot as we are today, looking to make
further policy adjustments in order to further extend the lifetime of
what remains of the IXP pool. Of course, space we will have wasted by
overassigning /26s until then will not be reclaimable, just like the
space we have already wasted by overassigning /24s until today is not.
This wasted space is permanently «stolen» from the future IX-es. If
that is what the IX community wants, then go for it! I do hereby
reserve the right to once again say «I told you so», though. ;-)

Tore