Many network operators have recently started to deploy their own Content Delivery Networks (CDNs) within their administrative domain. Having a CDN deployed within an operator's network has the advantage of potentially placing caches very close to the end user, thereby increasing Quality of Service for the user, while at the same time saving delivery costs for the operator. However, if each network operator hosts its own CDN, there is a need for interconnection among individual CDNs. The standardization of such CDN Interconnection (CDNI) hence has recently started in the IETF and ETSI.In this context, we present the first prototype implementation and evaluation of CDNI request routing facilitated by means of Application Layer Traffic Optimization (ALTO). By advertising network layer topology costs as well as conveying aggregated load on cache clusters, ALTO can enable an upstream CDN to select the best downstream CDN for each content request it intends to redirect. Our experiments study how-by using ALTO-upstream CDN can achieve cost savings while also taking the overall load of the downstream CDN into account.