Service Not Available
The service is not available and the control connection is being closed. Typically sent when the server is shutting down or overloaded.
421
421
Misdirected Request
The request was directed at a server that is not able to produce a response for the requested URI.
Extension Required
The server requires a specific extension that is not listed in a Supported header field in the request. The response includes a Require header indicating the needed extension.
Service not available
The server is temporarily unavailable and is closing the connection. The client should retry later.