HTTP 421 Misdirected Request vs 425 Too Early
Both HTTP 421 (Misdirected Request) and 425 (Too Early) belong to the 4xx Client Error category. 421 indicates that the request was directed at a server that is unable to produce a response for the combination of scheme and authority in the URI. Meanwhile, 425 means that the server is unwilling to risk processing a request that might be replayed. Used with TLS 1.3 early data (0-RTT).
Description
The request was directed at a server that is unable to produce a response for the combination of scheme and authority in the URI.
When You See It
With HTTP/2 when a connection is reused for a domain the certificate doesn't cover.
How to Fix
Retry the request on a new connection.
Description
The server is unwilling to risk processing a request that might be replayed. Used with TLS 1.3 early data (0-RTT).
When You See It
When a server rejects a request sent as TLS 1.3 early data due to replay risk.
How to Fix
Retry the request after the TLS handshake completes.
Key Differences
HTTP 421: The request was directed at a server that is unable to produce a response for the combination of scheme and authority in the URI.
HTTP 425: The server is unwilling to risk processing a request that might be replayed. Used with TLS 1.3 early data (0-RTT).
You encounter 421 when with HTTP/2 when a connection is reused for a domain the certificate doesn't cover.
You encounter 425 when when a server rejects a request sent as TLS 1.3 early data due to replay risk.
When to Use Which
For 421 (Misdirected Request): Retry the request on a new connection. For 425 (Too Early): Retry the request after the TLS handshake completes.