I want to know what IP ranges are belonging for example to the AS714.
How do I get this information?
I know how to do the reverse way, which is easy with whois. But the other way doesn't seem to be that easy.
Ok, I just found one simple way. You just put this http://bgp.he.net/[ASXXX]#_prefixes in your browser, where [ASXXX] is a certain AS and a number like this http://bgp.he.net/AS714#_prefixes.
They're listed online with related details at http://ipinfo.io/AS714 (replace the ASN to get the equivalent details for any other ASN).
If instead of browsing them you'd rather grab them programmatically you can use the RADb whois server: