In utorrent peers tab, i noticed peer, whose ip address was resolved to localhost.

When i disabled dns resolving, it displayed ordinary ip address (not .

How is it possible to make one's ip address resolve as "localhost" ?


Resolution of IP addresses to names is done by first converting the address to a special domain name ending with in-addr.arpa. or ip6.arpa. (for example, would be, then looking for PTR records on that domain, and using whatever results received as the final name.

These domains, however, work exactly like any other domain – there is no requirement that the PTR record points to a name that points back to the address, or to any address for that matter. The only validation, if any, is done by end software (μTorrent doesn't bother).

(There are no restrictions on the number or type of records, either – zero or multiple PTRs are legal. It's even possible, for the crazy, to host a website or receive mail on an arpa. domain.)

Corporate clients usually have direct access to rDNS of their own IP address blocks, while home users have to ask their ISP – which may implement some form of verification.

To test reverse DNS on Windows, you can use nslookup on the command line – either automatically:


or do the conversion yourself:

nslookup -q=ptr

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