While bandwidth for previous IP backbone networks deployed by Internet Service Providers typically has been limited to 34 Mbps, current and future IP networks provide bandwidth ranging from 155 Mbps to 2.4 Gbps. Thus, it is important to investigate the impact of emerging network technologies on the performance of cooperative Web caching protocols. In this paper, we present a comprehensive performance study of four cooperative Web caching protocols. We consider the Internet cache protocol ICP, Cache Digests, the cache array routing protocol, CARP, and the Web cache coordination protocol, WCCP. The performance of these protocols is evaluated using tracedriven simulation with measured Web traffic from NLANR. The goal of this performance study lies in understanding the behavior and limiting factors of the considered protocols for cooperative Web caching under measured traffic conditions. Based on this understanding, we give recommendations for Internet Service Providers, Web clients, and Application Service Providers.