HTTP 511 — Network Authentication Required
5xx Server Error
What it means
The client must authenticate to get network access — a captive portal on hotel or airport Wi-Fi.
What to do about it
Open a browser and sign in to the network. Nothing to fix on the server.
Where it sits
511 belongs to the 5xx family: The server failed to fulfil an apparently valid request. The fix is on the server side.
HTTP/1.1 511 Network Authentication RequiredChecking it yourself
# see the status code and headers only
curl -sI https://example.com/path
# follow redirects and print each hop
curl -sIL -o /dev/null -w "%{http_code} %{url_effective}\n" https://example.com/path
# JavaScript
const r = await fetch(url);
console.log(r.status, r.statusText);How this code behaves
| Cacheable by default | No — caches must not store this response unless explicit cache headers permit it. |
| Safe to retry | Yes, with backoff. This is a transient condition; retrying the same request is reasonable. |
| Effect on search indexing | Repeated server errors reduce crawl rate and eventually drop pages from the index. |
Returning 511 correctly
# nginx
return 511;
# Express
res.status(511).json({ error: 'Network Authentication Required' });
# Go
w.WriteHeader(511)
# Python (Flask)
return jsonify(error='Network Authentication Required'), 511;Frequently asked questions
What does HTTP 511 mean?
The client must authenticate to get network access — a captive portal on hotel or airport Wi-Fi.
How do I fix a 511 error?
Open a browser and sign in to the network. Nothing to fix on the server.
Is 511 a client or server problem?
A server problem. The request was valid; the server failed to fulfil it. Nothing the client changes will help.