4xx Client error
HTTP 421 Misdirected Request
The request was sent to a server that isn’t able to produce a response for this combination of scheme and host name. It typically happens when a browser reuses an HTTP/2 connection for another host name on the same certificate, but that server isn’t set up for it. The client may retry on a new connection.
//_01 Uptime checks
Is 421 up or down for a monitor?
Uptimecheck HTTP monitor
Default settings
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 421 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Is it down? checker
Free, at /is-it-down/
Up. The checker counts any answer below 500 as the site answering: a 421 comes from a server that is running.
//_02 Causes and fixes
Why you see 421 and what to do
Typical causes
- One certificate covering several host names that are served by differently configured servers.
- The TLS server name (SNI) not matching the Host header; Apache answers 421 for that.
If you run the site
- Make every host name on a certificate answer on every server that presents it, or use separate certificates.
If you’re a visitor
- Reload the page; the browser will open a new connection.
Know the moment your site stops answering as it should
An Uptimecheck monitor requests your page as often as every minute, checks the status code against the ones you expect, confirms a failure with a second check and then alerts you.
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Questions
What does HTTP 421 mean?
The request was sent to a server that isn’t able to produce a response for this combination of scheme and host name. It typically happens when a browser reuses an HTTP/2 connection for another host name on the same certificate, but that server isn’t set up for it. The client may retry on a new connection.
Does an uptime monitor count 421 as down?
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 421 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Downtime is obsolete.
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