What does HTTP status 451 (Iis Redirect) mean?

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: HTTP 451 is standardized for content that cannot be served for legal reasons.

Could be also:
Constant	Type	OS
ERROR_CAPAUTHZ_CHANGE_TYPE	Win32 error	Windows

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HTTP_STATUS_BLOCKED	HTTP_STATUS_REQUEST_HEADER_TOO_LARGE

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.

Treat 451 as a legal restriction

The standardized 451 response is intended to make legal blocking distinguishable from an ordinary 403 or 404. Implementations can include information about the legal demand or blocking entity when appropriate. Clients should not assume that changing credentials will help, because the restriction concerns legal availability rather than authentication.

RFC 7725: An HTTP Status Code to Report Legal Obstacles

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