The HTTP Status Code 421 means that a server that is not able to produce a response.
The status 421 can be the result of a connection refusal, for example.
Frequently Asked Questions
What does the HTTP 421 status code mean?
HTTP 421 Misdirected Request is a client error response indicating that the request was directed to a server that is not configured to produce a response for the combination of scheme and authority included in the request URI. The server is not refusing the request outright — it is signaling that this particular connection is the wrong channel for it. The client's expected remedy is to retry the request over a different connection.
When does a server return a 421 response?
A server returns 421 most often when HTTP/2 connection reuse causes a request for one domain to arrive on a connection that was originally established for a different domain. This typically happens with wildcard TLS certificates or connection pooling across multiple hostnames that share the same IP address. The server recognizes it cannot legitimately produce a response on that connection and issues the 421 to tell the client to start fresh.
What is the most common root cause of a 421 error?
The most common trigger is a mismatch between the Server Name Indication (SNI) value negotiated during the TLS handshake and the Host header in the HTTP request. When a single SSL certificate covers multiple domains and connections are reused across those domains, the SNI presented at connection time may not match the host the request is actually targeting. This mismatch causes the server to reject the request with a 421.
How do I fix an HTTP 421 Misdirected Request error?
On the client side, retrying the request over a new, dedicated TCP/TLS connection rather than reusing an existing multiplexed connection is the standard fix. On the server side, verify that TLS certificates cover every hostname the server handles and that SNI forwarding is correctly enabled in any reverse proxy configuration. For CDNs and load balancers, ensure upstream TLS handshakes send the correct SNI value so the origin can match the request to the right virtual host.
What is the difference between a 421 and a 400 Bad Request?
A 400 Bad Request means the server understood the connection but found the request itself malformed — for example, invalid syntax or a missing required header. A 421 Misdirected Request means the request is structurally valid but arrived on the wrong connection: the server is simply not configured to respond to that host on this particular channel. Fixing a 400 requires correcting the request content, while fixing a 421 requires establishing the correct connection.
Does a 421 status code affect SEO?
Yes. Pages that consistently return a 421 cannot be indexed by search engines, and URLs that were previously indexed may be removed from search results. Because the error signals a connection routing problem rather than a permanent content removal, it is important to resolve the underlying TLS or connection-pooling misconfiguration promptly so crawlers can access and index the affected pages normally.
