I have tried to follow this discussion, and stumbeled over a fundamental question when trying to reason about this:
* why are exchange points so special?
My take on this is that "they are not". But before plunging on, I would find it useful to distinguish between the two portions that have been discussed so far: o Addresses for the exchange point medium itself (usually a layer-two network of some sort) o Addresses for a "service network", probably used by the organization which runs the exchange point and which can provide additional common services of interest to the connected networks. I'll also mention that my experience on the matter is based on IPv4, so if there are additional quirks that are specific to IPv6 that I don't know about, you'll have to excuse me. For the exchange point medium itself, if the medium is a "multiple- access broadcast network" it *is* actually a benefit to use the "natural" way to number such networks, i.e. use a single IP subnet, as in that case you can use BGP in the "standard configuration". Starting to muddle with secondary IP addresses and run "multiple subnet on the same layer-two medium" when you in reality don't have to, just causes extra complications, and should therefore be avoided. If your exchange point is implemented using a "multiple- access non-broadcast network" of some sort, the multiple point-to- point links, each with their own subnet out of a connected peer's address block makes sense. Some have said that the IP network used to number the exchange itself does not have to be announced on the global level. However, it would appear that practices vary quite widely on this point for IPv4, and many are announced globally. You mention the possible use of link-local addresses; I wonder if that won't make it difficult to handle such things as ICMP; it'll probably be met with similar issues as folks who use RFC 1918 addresses in today's network (e.g. breaking Path MTU discovery because RFC 1918-originated datagrams are often summarily dropped on the floor). I may have misunderstood something fundamental, but I also don't quite know what's so bad with using IP(v4) addresses out of a provider's block to number the exchange point medium. As for the "service network", it will of course need global connectivity, and thus has to get transit service from one or more ISPs. What I don't understand is why this service network needs to be so special up and above other normal customers when it comes to IP address assignment? Creating these "special cases" as exceptions to the rules just opens up the floor for other folks who will stand up and say "My Cause is Extremely Worthy too, so I want some too under those conditions!!". Best regards, - Håvard