The Request Routing Interface comprises of (1) the asynchronous advertisement of footprint and capabilities by a downstream CDN that allows a upstream CDN to decide whether to redirect particular user requests to that downstream CDN; and (2) the synchronous operation of an upstream CDN requesting whether a downstream CDN is prepared to accept a user request and of a downstream CDN responding with how to actually redirect the user request. This document describes an interface for the latter part, i.e. the CDNI request routing/ Redirection Interface.