The decision of request mapping-which server to handle user request and response routing-which transit route to carry response back to user has great impact on the performance and cost of Content Delivery Networks (CDNs). Request mapping and response routing are traditionally treated independently. The information invisibility and inconsistent objectives may lead to worse performance and high cost. However, the rapid globalization of Internet eXchange Points (IXPs) has facilitated the cooperation between CDN and ISP. In this paper, we consider request mapping and response routing jointly. We formulate the joint problem to navigate the performance and cost tradeoff. To solve the large-scale optimization, we develop a distributed tide algorithm based on Gauss-Seidel. The joint problem can be decomposed to sub-problems which allows for a parallel implementation. Experiment result shows that the relative error between our distributed tide algorithm that iterates within 50 rounds and theoretical optimum is about 0.7 percent. Furthermore, the parallel runtime demonstrates the efficiency of our algorithm.