In general, techniques are described for managing content request referrals by keying content requests to a composite key data structure that maps end-user address prefixes and content identifiers to content delivery network servers of downstream CDNs. In one example, a CDN exchange includes a communication module to receive first network prefixes and first content identifiers from a first secondary content delivery network and to receive second network prefixes and second content identifiers from a second secondary content delivery network. A request router of the CDN exchange redirects the content request to the first secondary content delivery network or to the second secondary content delivery network according to a network address of the end user device and a content identifier for the content request.