Dyn offers a free web IP detection tool for use with DynDNS services. CheckIP will return the remote socket’s IP address. If a client sends a Client-IP or a X-Forwarded-For HTTP header, CheckIP will return that value instead.

  • Hostname: checkip.dyndns.org
  • HTTP ports: 80, 8245

Call and Answer

CheckIP responds to valid HTTP requests for http://checkip.dyndns.com/. A valid request will result in the following sample response:

HTTP/1.1 200 OK
Content-Type: text/html
Server: DynDNS-CheckIP/1.0
Cache-Control: no-cache
Pragma: no-cache
Content-Length: 105
Connection: close
<html><head><title>Current IP Check</title></head><body>Current IP Address: 123.456.78.90</body></html>


  • Use the OS if possible for IP detection
  • Checks must be spaced 10 minutes apart to help reduce server load
  • In the case of an error while accessing CheckIP, the client should not send an update

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