A node that is not a part of any user-defined logical server is implicitly a member of the OPEN logical server. The OPEN logical server consists of all multiplex nodes that are not members of any user-defined logical servers.
You cannot directly manipulate membership of a multiplex node into the OPEN logical server; it changes implicitly when you add multiplex nodes to, or drop them from, user-defined logical servers. The OPEN logical server may be empty when each server of a multiplex is a member of one or more logical servers.
The OPEN logical server supports these use cases:
A large multiplex deployment is likely to have some applications that require provisioning of their own resources. It is also likely to have other applications that are used in an ad hoc manner, and do not require dedicated resources. These ad hoc applications can be served by the OPEN logical server, rather than by user-defined logical servers.
In a utility computing environment where resources are used on a chargeback basis, you can keep the OPEN logical server empty as all applications and users access the multiplex with their assigned logical servers.