HTTP Status Code 511 refers to Network Authentication Required. This status code indicates that the client needs to authenticate to gain network access. It's often used by proxy servers to signal that the client must provide authentication credentials before it can access the requested resource.
When a client receives a HTTP Status Code 511, it means that there's a need for user authentication, typically through a login page or similar mechanism. This code is part of the HTTP protocol's extension for better handling of situations where network access is restricted.