5xx Server Errors
HTTP 511 Network Authentication Required
The client needs to authenticate to gain network access (captive portal).
When is 511 used?
- Airport WiFi captive portals
- Hotel/internet cafe login pages
How to handle a 511 response
The problem is on the server side. Check server and proxy logs, retry idempotent requests with exponential backoff, and alert on sustained 5xx rates.
Check the status code a URL returns from the command line:
curl -s -o /dev/null -w "%{http_code}\n" https://example.comHow to return 511 from your server
Node.js (Express)
res.status(511).json({ message: 'Network Authentication Required' });Python (Flask)
return {"message": "Network Authentication Required"}, 511Go (net/http)
w.WriteHeader(511)Frequently Asked Questions
What does HTTP 511 mean?
511 Network Authentication Required: The client needs to authenticate to gain network access (captive portal).
Is 511 an error?
Yes. 511 is in the 5xx Server Errors class. Server errors: the server failed to fulfil an apparently valid request.