As Brian said there is no central authority. The formula is based off your MAC address.
From memory it simply does HEX to decimal conversion for each of the
last 3 octets.
I found this: http://bloodhound.aredn.org/products/AREDN/wiki/TechRef/GUI/admin/PerlUI_IP_...
The ham meshnet folks use net 10 internally; they assign the addresses by a formula. They don't have a central IP authority. I don't recall the exact formula and whether it's based on an encoding of the callsign or the location of the station, but it was explained in a paper they published in a past TAPR DCC, either 2013 or 2014.
- Brian