How can I determine who is responsible for a particular IP address or domain?

Sometimes you may want to find out who is responsible for a particular IP address or domain name. For example, if you are getting junk mail from several email addresses that end in @mango.net, you may want to get an address for the system administrators at Mango Net to ask them to stop this. Or, if you think your computer has been broken into by another computer having the IP address of, for instance, 129.79.5.140, then you may want to find out what organization is responsible for that IP address.

If you are a student, faculty member, or staff member of Indiana University who needs access to IU's central systems from a computer outside the IU network, you may need to contact the outside system's network administrator for help. Receiving a bad IP address is the most common reason for needing to contact an outside network administrator. For example, if you dial into a local Internet service provider called Mango Net, and you are unable to access your IU email account, Mango Net may have assigned you a bad IP address. The Mango Net system administrators will need to fix this for you.

The American Registry for Internet Numbers (ARIN) provides a Whois utility that you can use to find the system administrator of a particular IP address or domain. You can access this utility at: http://www.arin.net/tools/index.html Enter the IP address or domain IP address in which you are interested.

An example of an IP address is: 129.79.8.50 This would be the IP address for a particular computer at IU.

An example of a domain IP address is: 129.79.0.0

All computers that start with 129.79 are in the indiana.edu domain.

Domain IP numbers can be of variable length. For example, for a small organization, the domain IP address might be: 198.88.16.0 A very large organization needing more individual IP addresses might have a domain IP address of just: 109.0.0.0

Also see:

• In Unix, how do I look up IP addresses?
• In Unix, how can I find out the domain name associated with an IP number?
• What is DNS?
• In Windows, how do I check my computer's IP address or physical (aka MAC) address?
• What are private IP addresses, and what are the reserved ranges?