You can generally get info about netblocks from whois (eg whois 128.151.162.17 refers to CIDR: 128.151.0.0/16), but you'll probably find that there's some variation in the format of the responses you get depending on which registry is involved, and also that whois servers are likely to cap the number of requests you can make.  Also note that netblocks are typically nested with smaller ones inside larger ones, and so you may get info about multiple netblocks for one IP.

A DNS request packet can contain multiple requests, which may speed things up if you need to resolve a lot of requests, but the main techniques you need are to paralellise requests, and to cache responses.

Get IP network range after reverse DNS?

  The eagle flies at midnight.


What's the origin and meaning of this idiom?
