How can I determine which company an IP address belongs to?

Question

I'm trying to programmaticaly determine the company* associated with a given IP address.

My first guess was this :

  string hostname = Dns.GetHostEntry(IPAddress.Parse(ip)).HostName;

but this won't work if the reverse DNS isn't set correctly, which seems to happen 90% of the time.

However some websites are still able to successfully determine the company associated with a specific IP even if the reverse dns fails. For example, on this site, the ISP Provider field sometimes contains valuable information (ie the name of the company) even if the hostname isn't set.

What's the easiest way to achieve the same thing using .net ?

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Notes :

• I don't need a canonical name. ie MS or Microsoft are both ok.
• I'm targeting big companies, which are likely to "own" their IP address ranges.
• I'm running on Windows, so unix's whois tools are not installed by default.

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Edit regarding the use of whois : Sometimes, there's no whois information associated with an IP

Answer 1

You can install the whois command line tool for windows from microsoft

edit: then what information are you looking for ?

>whois bbc.co.uk
Domain name:
    bbc.co.uk

Registrant:
    British Broadcasting Corporation

Registrant type:
    UK Limited Company, (Company number: 000057)

Registrant's address:
    Research & Development
    Kingswood Warren
    Tadworth
    Surrey
    KT20 6NP
    United Kingdom

Registrar:
    British Broadcasting Corporation [Tag = BBC]