The client must authenticate to gain network access, for example on a captive portal.
Quick facts
When does it occur
The client must authenticate to gain network access, for example on a captive portal.
It belongs to the 5xx Server Error class of responses, defined in RFC6585#6.
Browse all codes in this class: 5xx Server Error
Common causes
Frequently asked questions
511 belongs to the 5xx Server Error class and is generally not cached for long; behavior is controlled by Cache-Control.
5xx Server Error: The client must authenticate to gain network access, for example on a captive portal.
Sources & standards
Updated 2026-09-13
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