Speaking for myself too: I have been wanting an *authoritative* *single* listing of unallocated address space for at least 6 years. Note that this is at a finer granularity than the IANA allocations list and it would have much more frequent changes than the IANA list as address space is allocated to local registries. However it could include a more coarse data set that changes less frequently for those that do not want or need the higher granularity. The only way to make this happen is for the RIRs to collect this data among themselves and publish it regularly. Because of the possible ramifications of errors in this list it is not as simple to do that reliably as it may seem at first glance; but it should be done. I know that the RIRs have efforts underway to publish such authoritative lists. I do not know the exact status of this work. But I fully agree with your requirement for a *single* *authoritative* list. Of course I would use it in the routers I operate. However these are not significant to many peoiple these days. Daniel PS: I do not care at all about the format as long as it is readily machine parseable. Daniel