Error 421

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• Common use cases
• Cloudflare-specific information

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The 421 Misdirected Request status code indicates that the request was directed to a server that is not able to produce a response for the combination of scheme and authority included in the request URI.

For more details, refer to RFC 9110.

Common use cases

This error commonly occurs in HTTP/2 and HTTP/3 environments where connection reuse or alternative service selection is involved. A server may return a 421 response when:

• The Host header value does not match the SNI (Server Name Indication) used during the TLS handshake, causing the server to reject the request as misdirected.
• A single HTTP/2 connection is reused (coalesced) across multiple origins, but the server is not configured to respond for one of those origins.
• The client selected an alternative service (via the Alt-Svc header) that cannot handle the request for that specific scheme and host combination.

Upon receiving a 421, the client may retry the request on a new connection.

Cloudflare-specific information

Cloudflare may generate or forward a 421 response in several scenarios:

• SNI mismatch: The most common cause. If the SNI value used during the TLS handshake does not match the Host header in the HTTP request, Cloudflare returns 421 directly. Ensure your TLS certificate covers all hostnames you intend to serve — for example, use a wildcard or SAN certificate.
• Connection coalescing: Cloudflare may coalesce HTTP/2 or HTTP/3 connections across multiple origins. If the origin is not configured to serve all coalesced hostnames, a 421 results. Verify that your origin correctly handles all domain names sharing a connection.
• Cloudflare Tunnel: A 421 can occur if the tunnel ingress rule hostname does not match the request's Host header. Review your tunnel ingress configuration.
• R2 and Workers custom domains: A mismatch between the custom domain TLS SNI and the requested hostname can produce a 421. Verify that the custom domain is correctly configured and that the TLS certificate covers the relevant hostname.

If you receive a 421, retry the request on a new connection with the correct SNI and host combination.