421
Client Error
421 Misdirected Request
The request was directed at a server that cannot produce a response for that combination of scheme and authority.
Description
421 Misdirected Request (RFC 7540) indicates that the request was directed at a server that is not able to produce a response for the combination of scheme and authority included in the request URI. This is primarily relevant in HTTP/2 connections where multiple domains may share a single connection (connection coalescing).
Common Causes
- HTTP/2 connection coalescing routing request to wrong virtual host
- TLS SNI mismatch — request for domain not covered by the server's certificate
- Load balancer misconfiguration routing to the wrong backend
- CDN or reverse proxy serving different domains on shared connections
How to Fix
- Retry the request on a new connection
- Check TLS certificates cover all expected domains (SAN entries)
- Review load balancer and proxy routing rules
- In HTTP/2, disable connection coalescing if it causes misrouting
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