How to determine the country by ip address?

Question

SQL

Good night everyone, I'm interested in such a question, how best to implement the definition of the country by IP address, then saving it in the ISDB? (you can use asp.net, c#, JS(query), mssql)
For example (to avoid questions "why?"): for the registration form. Without any fields, they say, select your country, but for it to be in the background :)

Answer 1

google -> geoip
maxmind has API under .net