Via Tools -> Administration -> Computing Center -> Management System -> Configuration -> Logon Groups (transaction SMLG), you can group together servers to logon groups. Logon groups allow an automatic and load-dependent distribution of users to the servers that belong to a logon group.
The SAPGUI frontend server provides supports for logon groups. A user can determine the available classes and log himself on to a class or directly to the SAP server. According to the load distribution mechanism, the user is automatically logged on to the server with the least load with this logon procedure.
Computing Center Management System enhancements. You can alternatively change the organization and execute the logon procedure.
Please refer to the SAP manual Computing Center Management System for more information on logon groups.