511 Network Authentication Required
The client needs to authenticate to gain network access (captive portal).
Definition (RFC 6585)
HTTP status code 511 511 Network Authentication Required is defined in RFC 6585 (Additional HTTP Status Codes), not in RFC 9110. RFC 9110 defines the core HTTP status codes; this one was registered separately in the IANA HTTP Status Code Registry.
Description
511 Network Authentication Required (RFC 6585) indicates that the client needs to authenticate to gain network access. This is commonly generated by intercepting proxies used to control access to the network — such as Wi-Fi captive portals in hotels, airports, and coffee shops.
When a client encounters a 511, they should be redirected to a login/acceptance page. This code should not be used by origin servers — only by network-level proxies.
Common Causes
- Public Wi-Fi captive portal requiring login (hotel, airport, café)
- Corporate network access control requiring VPN authentication
- ISP requiring agreement to terms of service
- Network firewall intercepting HTTP traffic before authentication
How to Fix
- Open a browser and navigate to any HTTP URL to trigger the captive portal login page
- Complete the authentication or terms acceptance on the captive portal
- Use HTTPS connections (HSTS) to detect captive portal interference
- For developers: never return 511 from origin servers — only from network proxies
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