g to managed resources is often stored in a physical database, this database is often spoken of as the MIB. 1. Only do all operations if they can be successfully completed, The MIB provides a method for relating managed objects to each otherwise to do none of them ('atomic' action). other. It is by manipulation of the virtual object held within the MIB 2. Do as many operations as it can complete ('best effort' action). that the real database held within the node can be examined or changed. In addition to the above solicited requests, unsolicited reports may The Management Information Base (MIB) contains a virtual be received by the manager from the managed object. This is image of how a network is behaving at any time. It should not be achieved by means of the CMIS EVENT-REPORT service, which confused with the configuration databases, which are located at allows the agent to send events and alarms. management centres and which keep information on how the node A complex system would have several managers and several should be behaving. The MIB must span all seven layers, as shown agents. A manager can be a managing process for its own agents and in Figure 16.15(a), since it must be able to access and change the an agent for another managing process. Managers and agents can management information in all layers of the stack. A problem can therefore form a hierarchy of management domains, as shown in arise when controlling devices which do not have a full seven layer Figure 16.14, each domain defining the scope of its manager. implementation, such as modems, bridges and routers. Two solu- tions are possible in these instances: use of a thin stack, or of a proxy node (translator node). 16.7.3 The Management Information Base Figure 16.15(b) shows a device which uses a thin stack. In this arrangement the device which does not have the full seven layers The set of managed objects, made visible by the agent to the only performs the minimum functionality needed to support net- manager, is called the Management Information 