Google DNS Geo Location – How Does Google Do DNS Geo Location Request Routing?

There are patches available to do GeoIP in various DNS servers.

Bind: http://www.caraytech.com/geodns/

Good writeup of Bind patches, includes RPMs: http://www.devco.net/archives/2006/07/11/location_aware_bind.php

djbdns: http://www.anders.com/cms/276/tinydns.GeoIP.patch/djbdns/Geographically.Aware

Also interesting is this hack, which involves not patching Bind: http://phix.me/geodns/

It should still be pretty solid. Once an ISP has a block of IP addresses, it's usually pretty reluctant to relinquish it, so only those that have gone under will have returned their allocations.

Most of the early /8 allocations will still be attached. The RIRs will have kept all of theirs, too, so you'll have good accuracy at the continental level. It's difficult to estimate how many LIRs will have relinquished theirs and what churn there is will be at the smaller ISP level.

The NRO has some good stats on allocations, but not much about recovery rates: http://www.nro.net/statistics

If you really want to delve into it, the RIRs maintain FTP sites with historical allocation data in them, such as: ftp://ftp.ripe.net/pub/stats/ripencc/

My guess is that, if you believe MaxMind's claim of 99.5% accuracy on their current, public DB, you'd still get ~95% on 3-year old data.