* David Farmer
So, if an IXP starts with three(3) participants, per policy, with a /29, it is already at 50% full, leaving 3 addresses for growth, and that doesn't include any infrastructure IP addresses, like a route server(s), etc...
Exactly, a tiny IXP with three founding members would have enough space to double in size before needing to renumber out of an initial /29. For a slightly larger IXP with six founding members (or four founding members + two route servers and so on), the situation would be exactly the same - it would have enough space to double in size before needing to renumber out of an initial /28. And so on… (BTW: «founding member» here means «connects within the first year»)
Therefore, starting at a /28 makes more sense to me. Forcing most IXPs to renumber almost right out of the gate doesn't make much sense to me.
It seems that you assume here that all/most IXPs will grow out of an initial /29 and therefore require renumbering «right out of the gate». If that was the case, I would not suggest /29 as the default. However, Matthias's numbers seem to suggest otherwise, with plenty of IXPs (~25%) managing just fine with a /29. This does not surprise me all that much. If you set establish IXP in some rural location (in Longyearbyen, let's say), there is an almost zero percent chance there will be more than six members connecting in the foreseeable future because there are so few operators servicing that area. While AMS-IX, DE-CIX, LINX, Netnod and the like are probably what springs to mind when one says «IX», it would appear that behemoths like those are exceptionally rare and few in numbers compared to the small ones with just a handful of members, and I think it would be wise to keep that in mind when developing this policy further. Anyway, for the IXPs that *would* grow out of an /29, it's not like renumbering is *that* hard. Current policy grants 180 days to complete the renumbering, and when the IXP is just 4-5-6 members, it would even be doable to just gather everyone on a teleconference call and just do it all together.
Finally, maybe there should be a maximum allocation size of /24.
Policy currently has a maximum limit of /22, for what it is worth. So even the behemoth IX-es with up to 1K members are catered to by this policy. I'm fine with that. Tore