In a multiplex, you can only access servers by using logical servers.
Not all member nodes may be available at all times to its logical server for reasons such as a failure or exclusion of a member node from the multiplex. At any given time, the effective logical server configuration represents the current dynamic constitution of the logical server consisting of all member nodes that are actually available for use to the logical server. The effective logical server configuration is essentially a function of static logical server configuration and dynamic state of the multiplex.