511 - Network Authentication Required
HTTP 511 Network Authentication Required means the client must authenticate to gain network access, often through a captive portal.
Last reviewed: February 25, 2026|Editorial standard: source-backed technical guidance
What Does Network Authentication Required Mean?
Network access is blocked by an intermediary policy (typically captive portal), so application requests fail until the user/device authenticates at network level.
Common Causes
- -Captive portal intercepts outbound traffic and requires interactive network login before internet access is granted.
- -Wi-Fi gateway session tied to device MAC expires, and non-browser API client cannot re-authenticate automatically.
- -Network access control policy injects authentication-required responses for unregistered devices on corporate VLAN.
How to Fix Network Authentication Required
- 1Detect captive portal or network-gateway challenge and complete required network login flow.
- 2Re-establish network session (Wi-Fi re-auth, enterprise NAC check, guest portal acceptance) before retrying API calls.
- 3Separate network-auth handling from API credential handling to avoid misclassifying 511 as app-level auth failure.
Step-by-Step Diagnosis for Network Authentication Required
- 1Capture response headers/body from network intermediary to identify captive portal or NAC enforcement path.
- 2Verify whether issue reproduces only on specific networks, SSIDs, proxies, or device postures.
- 3Check session expiry, MAC/device registration, and policy compliance states at network controller.
- 4Retest after successful network authentication and confirm application endpoints no longer return 511.
Captive Portal and Network Policy Detection
- -Identify intermediary challenge patterns (example: hotspot redirects all HTTP requests to portal login page).
- -Validate network access-control policy state (example: device quarantine VLAN until endpoint compliance check passes).
Session Lifecycle and Client Connectivity Checks
- -Inspect session timeout and re-auth cadence (example: guest network session expires every 8 hours, then APIs return 511).
- -Test connectivity outside app stack (example: simple browser probe to detect portal interception before API retries).
Implementation Examples
curl -i -X GET https://api.example.com/v1/resource
# Response:
# HTTP/1.1 511 Network Authentication Required
# {"error":"Network Authentication Required","code":"511"}const response = await fetch('https://api.example.com/v1/resource', {
method: 'GET',
headers: { 'Accept': 'application/json' }
});
if (response.status === 511) {
console.error('Handle 511 Network Authentication Required');
}import requests
response = requests.get(
'https://api.example.com/v1/resource',
headers={'Accept': 'application/json'}
)
if response.status_code == 511:
print('Handle 511 Network Authentication Required')How to Verify the Fix
- -Re-run affected requests after network authentication and confirm 511 no longer appears.
- -Validate network session remains active across expected roaming and idle intervals.
- -Confirm app telemetry now distinguishes network-auth failures from API-auth failures.
How to Prevent Recurrence
- -Implement explicit captive-portal detection in clients before API traffic begins.
- -Expose user guidance and automated retries tied to network-auth completion events.
- -Monitor network-session expiry events and tune reconnect logic for managed devices.
Pro Tip
- -run a lightweight connectivity probe endpoint and gate API startup until probe confirms unrestricted network path.
Decision Support
Compare Guide
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Use 429 for caller-specific throttling and 503 for service-wide outages, so retry behavior, escalation paths, and incident ownership stay correct.
Compare Guide
500 Internal Server Error vs 502 Bad Gateway: Root Cause
Debug 500 vs 502 faster: use 500 for origin failures and 502 for invalid upstream responses at gateways, then route incidents to the right team.
Playbook
API Timeout Playbook (502 / 504 / DEADLINE_EXCEEDED)
Use this playbook to separate invalid upstream responses from upstream wait expiration and deadline exhaustion, and apply timeout budgets, safe retries, and circuit-breaker controls safely.
Playbook
Availability and Dependency Playbook (500 / 503 / ServiceUnavailable)
Use this playbook to separate origin-side 500 failures from temporary 503 dependency or capacity outages, then apply safe retry and escalation paths.
Official References
Provider Context
This guidance is specific to HTTP services. Always validate implementation details against official provider documentation before deploying to production.