The Grid aims at expanding the cluster based parallel computing paradigm toward large scale distributed systems based on IP networks. To validate grid algorithms, evaluate their performance and to study transport and coordination protocols and grid network services, a well controlled environment is required, allowing to precisely manage the ex- perience conditions. One of the most important issue is to emulate the potentially very high speed wide area network interconnection. This pa- per presents a software and hardware tool for con¯guring and program- ming a large PC cluster in a wide area network emulation instrument. High performance, ¯ne parameter tuning and a great utilization °exi- bility are the main proposed features of this experimental tool. This article discusses the eWAN design principles and the ¯rst experimenta- tions that have been done on a prototype deployed over the Grid5000 cluster at the ENS Lyon. Some usage scenarii are also proposed.