SIP (Session Initiation Protocol) is the signalling protocol behind most VoIP systems. This tool sends a crafted SIP REGISTER request over UDP to a given host and port, waits for the response, and shows whether the endpoint is reachable, what it answers and how fast.
Fill in the host, the UDP port (5060 by default; also 5061 for TLS, 5069 for some providers) and an optional user handle. The tool opens a single UDP datagram session from our server and displays both the request sent and the response received.
Common SIP response codes
- 100 Trying / 180 Ringing — provisional, the server accepted the request.
- 200 OK — success, the endpoint is alive and healthy.
- 401 Unauthorized / 407 Proxy Authentication Required — the server is up and is asking for authentication (which is normal for REGISTER).
- 404 Not Found — SIP stack is healthy but doesn't know that user.
- No reply — the port is silently dropped or the server is offline.
FAQ
Which port should I use? 5060 for plain UDP/TCP is the default. 5061 for TLS. Providers sometimes move the public port (5069, 5070) to hide from scanners.
Why a REGISTER probe? REGISTER is the lightest SIP message a server must answer to prove it's operational, even if anonymously.
What does 401 mean here? 401 is a good sign — the SIP stack is healthy and is refusing authentication for the anonymous probe, as expected.