The interconnection of Content Distribution Networks (CDNs) is predicated on the ability of downstream CDNs (dCDNs) to handle end- user requests in a functionally equivalent manner to the upstream CDN (uCDN). The uCDN must be able to assess the ability of the dCDN to handle individual requests. A CDN interconnection (CDNI) interface is needed to facilitate the advertisement of capabilities by the dCDN to the uCDN. This document describes an approach to implementing a CDNI capabilities advertisement interface.