Misdirected Request
The request was directed at a server that is not able to produce a response.
What it means
The HTTP 421 Misdirected Request client error response code indicates that the request was directed at a server that is not configured to produce a response for the destination URI.
This is primarily used in HTTP/2 where connections are multiplexed and reused. If a client reuses an existing connection for a different domain, but that specific server node doesn't host that domain, it returns 421.
How it works
- 1A client has an open HTTP/2 connection to IP 1.2.3.4 for 'a.com'.
- 2The client wants to visit 'b.com' which also resolves to 1.2.3.4, so it reuses the connection.
- 3The server behind 1.2.3.4 actually routes 'b.com' elsewhere and can't handle it on this connection.
- 4The server returns 421.
Why you're seeing this
- • Aggressive connection reuse in HTTP/2/3.
How to fix it
- • Browsers automatically catch the 421 error, open a brand new TCP/TLS connection for the new domain, and retry the request transparently.
Framework Implementations
Nginx
# Mostly handled by HTTP/2 server implementations internally.
Real-Life Scenarios
This is handled automatically by reverse proxies (like Nginx/HAProxy) in HTTP/2 environments. Application developers never throw this.
HTTP/2 Connection Coalescing
A browser tries to aggressively optimize connections by coalescing requests to different subdomains over a single TCP connection, but the server infrastructure doesn't support it.
HTTP Transaction
1. Client Request
GET / HTTP/2 Host: b.com (Sent over an existing connection for a.com)
2. Server Response
HTTP/2 421 Misdirected Request
SEO Implications
None.