How to determine nationality based on IP address?

Question

How can I tell the nationality of a user of my web site based on client ip?

Edit: Like commented, this question have been answered before:

https://stackoverflow.com/questions/283016/know-a-good-ip-address-geolocation-service

Answer 1

use the GeoIP databse. there is a free one. there are also a lot of GeoIP webServices you can use.