421 Misdirected Request

The 421 Misdirected Request is an HTTP status code that indicates the server cannot produce a response for a request. This status code is typically used when the server is unable to process the request due to its configuration.

Understanding the 421 Misdirected Request Status Code

The 421 Misdirected Request status code was introduced in HTTP/2 and is defined in RFC 7540. It signifies that the server is not able to produce a response for the client’s request, as the request was directed at a server that is not able to generate the appropriate response. This can occur when the server is misconfigured or when the client has reused a connection to a different server.

When is a 421 Misdirected Request Status Code Used?

The 421 Misdirected Request status code is used in the following scenarios:

1. Server Misconfiguration: The server receiving the request might be misconfigured, causing it to be unable to generate the appropriate response for the client’s request.
2. Connection Reuse: A client might reuse a connection to a different server, causing the request to be sent to the wrong server. This can happen when using HTTP/2 connection coalescing or when a client reuses a connection from a previous request.

Example of a 421 Misdirected Request

In this example, the client sends a request to a server that is misconfigured and cannot generate the appropriate response.

GET /example-resource HTTP/2
Host: example.com

The server responds with a 421 Misdirected Request status code, indicating that it cannot process the request.

HTTP/2 421 Misdirected Request
Content-Type: text/html; charset=utf-8
Content-Length: 0

How to Resolve a 421 Misdirected Request Status Code

To resolve a 421 Misdirected Request status code, you can take the following steps:

1. Check Server Configuration: Review the server’s configuration to ensure that it is set up correctly to handle the requested resource. Make sure that the server is properly configured to handle the specific domain and resource requested by the client.
2. Disable Connection Reuse: If the issue is due to connection reuse, consider disabling connection reuse or implementing connection coalescing correctly. This can be achieved by configuring the client to use a new connection for each request or by ensuring that the server is configured to handle requests for all the domains that the client might reuse connections for.
3. Use HTTP/1.1: If the issue persists and you are using HTTP/2, consider downgrading to HTTP/1.1, as the 421 Misdirected Request status code is specific to HTTP/2. However, please note that this might have performance implications and should be considered a last resort.

Summary

In conclusion, the 421 Misdirected Request status code indicates that the server cannot produce a response for a request due to its configuration or connection reuse. To resolve this issue, you can check the server’s configuration, disable connection reuse, or downgrade to HTTP/1.1.