Open Resolver Check Site

JPCERT/CC has been observing situations where open DNS resolvers are spread widely across Japan. 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.

Query “” will be conducted on the source

Note: It may take time when the server is under heavy load. Please click the "Submit" button again if the site does not redirect you to the result page.
* This site consider the IP address that sends DNS query to this site as the full resolvers, hence some of them might not be listed because of reasons including stateless UDP packet may be missing.
* When full resovlers uses different IP addresses to send queries to the authoritative DNS servers than that receive queries from your PC, this site consider the former addresses as the full resolvers, so that they might be different from settings in your PC.
* When your browser resolves name via DNS over HTTPS and similarities, this site considers the actually query-sending IP address as full resolvers and show results for them.

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. "curl" command).

Try check site using command lines at the following URL:

The graphs are created based on data provided byThe Shadowserver Foundation. Note: The graphs do not show the total number of open DNS resolvers on the Internet. Please refer to graph data.