ErrorFindly
4214xx Client ErrorMedium

HTTP 421 Misdirected Request

Defined in RFC 7540

What Does HTTP 421 Mean?

The request was directed at a server that is not able to produce a response, typically due to HTTP/2 connection reuse to the wrong origin.

Common Causes

  1. 1HTTP/2 connection coalescing to wrong virtual host
  2. 2SSL certificate mismatch with requested hostname
  3. 3Load balancer routing to wrong backend
  4. 4CDN serving wrong origin due to shared IP

Impact

  • ⚠Page fails to load
  • ⚠SSL/TLS errors in browser
  • ⚠Intermittent connection failures

Developer Fix

For web developers and application engineers

  1. 1Ensure HTTP/2 connection reuse is configured correctly
  2. 2Verify SSL certificate covers all required domains
  3. 3Handle 421 by retrying on a new connection

Server Admin Fix

For system administrators and DevOps engineers

  1. 1Review virtual host configurations
  2. 2Ensure SSL certificates match all served domains
  3. 3Check HTTP/2 connection coalescing settings
  4. 4Verify load balancer routing rules

Frequently Asked Questions

Why does 421 happen with HTTP/2?
HTTP/2 allows reusing a single TCP connection for multiple domains if they share an IP and SSL certificate. If the server can't handle a request for a domain on that connection, it returns 421, telling the client to open a new connection.
How do I fix recurring 421 errors?
Check your SSL certificates cover all domains, verify virtual host configurations, and ensure your server properly handles HTTP/2 connection coalescing.

Related HTTP Status Codes

400Bad Request502Bad Gateway

About the Author

Web Infrastructure Team

Verified against official RFC specifications and real-world server configurations. HTTP status code behavior confirmed across Apache, Nginx, and Cloudflare.