In general, techniques are described for advertising end user content delivery reachability by content delivery networks (CDNs) to upstream content serving entities. In one example, a CDN interconnection (CDNI) device of a content serving entity receives a prefix advertisement that specifies a downstream entity and indicates the downstream entity provides content delivery reachability to the network address prefix. A request router of the CDNI device receives a content request that includes a request for content and specifies a network address of an end user device to receive the content, wherein the network address is within a range defined by the network address prefix. The request router selects the downstream entity to serve the content request based at least on the content delivery reachability indication and redirects the content request to the downstream entity.