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.
Definition (RFC 9110)
HTTP status code 421 421 Misdirected Request is defined in RFC 9110 (HTTP Semantics), Section 15.5.20 — the current authoritative specification for HTTP semantics, published June 2022, which obsoletes the older RFC 7231 and RFC 2616.
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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