Named Data Networking (NDN) is an emerging communication paradigm to resolve a traffic explosion problem due to repeated and duplicated delivery of large multimedia content. To make NDN being useful more widely, however, it should support various types of traffic and their Quality of Service (QoS) requirements. In this paper, we propose a differentiated services (diffserv) model for NDN. For scalability, the proposed diffserv model is designed to follow the guidelines from the IP diffserv model. Traffic classification and packet marking are performed at edge routers, and class based service differentiation is provided by core routers. The proposed model, at the same time, supports fascinating features of NDN for efficient content delivery such as interest aggregation and content caching. To demonstrate the proposed model more realistically, we implement and evaluate it on a CCNx testbed.