Multi-Protocol over ATM (MPOA) is being considered by the industry as an important short-cut technology that provides an efficient transfer of inter-subnet unicast data in a LANE environment. MPOA was initially considered to carry backbone traffic in the enterprise or campus networks. However, congestion in the public Internet provokes many to consider MPOA as a solution for the carrier or service provider networks as well. In this paper, we investigate the scalability issues of MPOA in the wide area network environment. We use a realistic simulation model driven by real Internet traffic traces to study crucial metrics such as the SVC setup rate, the number of VCs required, and the percentage of packets switched. Based on the simulation results, we find that MPC ingress cache size provides a three-way trade-off among the percentage of switched packets, the VC usage and the SVC setup rate requirement. We also find that the SVC setup rate is linearly dependent on the packet arrival rate...