How do Gateways and Realms on Battle.net work?
Gateways, or Realms in Diablo II, on Battle.net are divided into in four regions: Asia, Europe, U.S. West & U.S. East. The Gateways are named to clearly indicate where the closest Gateway server to you is located–directing you to the best connection and play experience. While it is best to choose the Gateway closest to your geographic location, you are not restricted to any particular Gateway. You can choose to connect to any Gateways.