The server and database activity monitoring log setup described in Chapter 20, Monitoring Server and Database Activity
is specific to Directory Server. You can also monitor your Directory Server using Simple Network Management Protocol (SNMP), which is a management protocol used for monitoring network activity which can be used to monitor a wide range of devices in real time.
Directory Server can be monitored with SNMP through an AgentX subagent. SNMP monitoring collects useful information about the Directory Server, such as bind information, operations performed on the server, and cache information. The Directory Server SNMP subagent supports SNMP traps to send notifications about changes in the running state of your server instances.
SNMP has become interoperable on account of its widespread popularity. It is this interoperability, combined with the fact that SNMP can take on numerous jobs specific to a whole range of different device classes, that make SNMP the ideal standard mechanism for global network control and monitoring. SNMP allows network administrators to unify all network monitoring activities, with Directory Server monitoring part of the broader picture.
SNMP is used to exchange data about network activity. With SNMP, data travels between a managed device and a network management application (NMS) where users remotely manage the network. A managed device is anything that runs SNMP, such as hosts, routers, and your Directory Server. An NMS is usually a powerful workstation with one or more network management applications installed. A network management application graphically shows information about managed devices, which device is up or down, which and how many error messages were received, and so on.
Information is transferred between the NMS and the managed device through the use of two types of agents: the subagent and the master agent. The subagent gathers information about the managed device and passes the information to the master agent. Directory Server has a subagent. The master agent exchanges information between the various subagents and the NMS. The master agent usually runs on the same host machine as the subagents it talks to, although it can run on a remote machine.
Values for SNMP attributes, otherwise known as variables, that can be queried are kept on the managed device and reported to the NMS as necessary. Each variable is known as a managed object, which is anything the agent can access and send to the NMS. All managed objects are defined in a management information base (MIB), which is a database with a tree-like hierarchy. The top level of the hierarchy contains the most general information about the network. Each branch underneath is more specific and deals with separate network areas.
SNMP exchanges network information in the form of protocol data units (PDUs). PDUs contain information about variables stored on the managed device. These variables, also known as managed objects, have values and titles that are reported to the NMS as necessary. Communication between an NMS and a managed device takes place either by the NMS sending updates or requesting information or by the managed object sending a notice or warning, called a trap, when a server shuts down or starts up.