Why would ARIN specifically provide such a list? ARIN is not responsible

for the unallocated space, and there is more in the world than just ARIN.

There are liability issues with that, not to mention the fact that it is more an IANA function (if for the sake of argument someone would implement the list).

I consider this to be more of a minor technical issue. ARIN can certain provide an authoritative directory for the unallocated portions of its own allocations. And to answer your why question; because only ARIN has an authoritative and up-to-date view of exactly which addresses are and are not allocated. Rob Thomas is doing some fine work but he is just plugging a gap created by inaction on the part of the RIRs. I'd like to see RIPE, APNIC and LACNIC also set up authoritative LDAP directories for unallocated IP space at the largest aggregate level. I'd also like to see them all dump the quirky and antiquated whois protocol and move to LDAP as the standard way of querying their directories. The details of which data goes in which directory and whether or not to use referral LDAP or mirrored databases is something which I'm not concerned about. We know a lot about running a distributed directory from experience with DNS so I'm sure that a distributed LDAP hierarchy for the IP address space won't raise any major issues. There is a lot of LDAP expertise out there in the world, lots of books, multiple implementations with years of production experience and people running LDAP directories on a much larger scale than we need. There is no question that it would work, we just need the will to prevail against these problems instead of throwing up our hands and claiming it's too hard, it's impossible and it's not my problem. --Michael Dillon