Forum Moderators: phranque
it's actually a very difficult problem.
here is a white paper on geolocation [ccsl.carleton.ca].
It's not 100& effective, however you may be assured of a good success rate.
It is time consuming to do this manually, however in the event that your task is far smaller eastern euro countries the ranges should be very small.
4-5 years ago I went through the entire APNIC ranges, denying the majority, while my goal was to allow access for the Oceanic countries.
The results remain implemented today, however I've even reduced access for some of the Oceanic countries.
Later (than 4-5 years ago) denial of access was added for the majority of RIPE ranges. An occasional new addition to registrar changes slips through, however for the most part remains effective.
AFRIC and LACNIC are denied as well.