Programming network processors remains an art due to the variety of different network processor architectures and due to little support to reason and explore implementations on such architectures. We present a case study of mapping an IPv4 forwarding switch application on the Intel IXP1200 network processor and we compare this implementation with an analytical model of both the application and architecture used to evaluate different design alternatives. Our results not only show that we are able to model the IXP1200 and our application within 15% of the accuracy compared to that of IXP1200 simulation, but also find closely matching trends for different workloads. This shows the clear potential of such analytical techniques for design space exploration.