What does HTTP status 451 (Iis Redirect) mean?

HTTP_STATUS_IIS_REDIRECT

A 451 response can explain the legal demand, policy, or jurisdiction involved and can identify the party responsible for the restriction. It is not a redirect even when an older platform label describes it that way.

For a site operator, preserve the legal notice and check the enforcement layer: origin application, CDN, hosting provider, or network filter. For a user, changing request syntax will not resolve a legal restriction.

RFC 7725: An HTTP Status Code to Report Legal Obstacles

Operational meaning of HTTP 451 for HTTP_STATUS_IIS_REDIRECT

HTTP 451 (HTTP_STATUS_IIS_REDIRECT) is a client-error response. AllStat records its meaning as “451 Redirect”. For HTTP_STATUS_IIS_REDIRECT, interpret it with the request method, selected representation, response headers, and the specification or product that defines the code; the number alone does not prove that application work completed.

Client and server handling for HTTP_STATUS_IIS_REDIRECT

• Treat HTTP_STATUS_IIS_REDIRECT as a condition visible at the request boundary; inspect authentication, syntax, preconditions, routing, and resource state before retrying.
• For HTTP_STATUS_IIS_REDIRECT, preserve the response body and challenge or retry-related headers because they often carry the actionable reason.
• For HTTP_STATUS_IIS_REDIRECT, automatic retry is safe only when the method and status contract allow it and the request has been corrected.

For telemetry, record HTTP 451, method, authority, route template rather than secrets, response headers relevant to caching or retry, latency, upstream identity, and whether the response originated at the application or an intermediary.

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