511 Network Authentication Required

What This Error Means

The client needs to authenticate to gain network access.

Network authentication required (captive portal).

Common Causes

• Captive portal at hotel/airport
• Public Wi-Fi authentication
• Network access control

How to Fix It (For Visitors)

• Open browser to authenticate
• Complete captive portal login
• Agree to terms of service

How to Fix It (For Developers/Admins)

• Implement captive portal detection
• Handle authentication flow
• Redirect to login page

Code Examples

Here's how to return a 511 status code in various programming languages:

Python (Flask)

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/endpoint')
def endpoint():
    return jsonify({"message": "Network Authentication Required"}), 511

Node.js (Express)

const express = require('express');
const app = express();

app.get('/endpoint', (req, res) => {
    res.status(511).json({ message: 'Network Authentication Required' });
});

PHP

<?php
http_response_code(511);
header('Content-Type: application/json');
echo json_encode(['message' => 'Network Authentication Required']);
?>

Go

package main

import (
    "encoding/json"
    "net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(511)
    json.NewEncoder(w).Encode(map[string]string{
        "message": "Network Authentication Required",
    })
}

Java (Spring Boot)

@GetMapping("/endpoint")
public ResponseEntity<Map<String, String>> endpoint() {
    Map<String, String> response = new HashMap<>();
    response.put("message", "Network Authentication Required");
    return ResponseEntity.status(511).body(response);
}

Ruby (Sinatra)

get '/endpoint' do
    status 511
    json message: 'Network Authentication Required'
end

Browser Compatibility

Browser	Support	Notes
Chrome	✓ Full Support	All versions
Firefox	✓ Full Support	All versions
Safari	✓ Full Support	All versions
Edge	✓ Full Support	All versions

Official Specification

This status code is defined in RFC 6585.

View on IANA HTTP Status Code Registry →