Open DNS Resolver Check Site

JPCERT/CC has been observing situations where open DNS resolvers are spread widely across Japan. Moreover, according to the survey conducted by the Open Resolver Project, there exist about 28 million open DNS resolvers throughout the world (as of Oct 2013). An open DNS resolver is a publicly accessible name server that provides a recursive name resolution for unspecified IP addresses. It has been reported that a number of open DNS resolvers are being exploited to participate in massive distributed denial of service (DDoS) attacks. JPCERT/CC has also been observing situations where not only host computers that operate as DNS servers but also network devices (e.g. broadband routers) unintentionally running open DNS resolvers.

This site allows you to check on the following 2 points:

- Whether the DNS server configured on your PC is running an open DNS resolver or not
- Whether your network device (e.g. broadband router) connecting to this site is running an open DNS resolver or not

JPCERT/CC appreciates your contribution towards a robust cyber space by utilizing this check site.
Please click the link below to check.
Check Open DNS Resolver.

JPCERT/CC has also received a number of reports where servers of hosting services are operating as open DNS resolvers, despite users' intentions. We have also set up another site for such host administrators to check their computers using command lines (e.g. "wget" command).

Try check site using command lines at the following URL:

The graphs are created based on data provided by The Shadowserver Foundation.
(Note: The graphs do not show the total number of open DNS resolvers on the Internet.)