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1.4 Elements of a Network Management Architecture

How does a network manager know what he or she is responsible for and then manage such a network? To answer these questions, you need to understand the architecture of a network management system and how it accomplishes its tasks.

The network management system, called the manager/agent model, consists of a manager, a managed system, a database of management information, and the network protocol (see Figure 1-4).


Figure 1-4.  Network manager/agent relationships

The manager provides the interface between the human network manager and the devices being managed. It also provides the network management process. The management process performs tasks such as measuring traffic on a remote LAN segment or recording the transmission speed and physical address of a router’s LAN interface. The manager also includes some type of output, usually graphical, to display management data, historical statistics, and so on. A common example of a graphical display is a map of the internetwork topology showing the locations of the LAN segments; selecting a particular segment might display its current operational status.

As Figure 1-4 shows, the managed system consists of the agent process and the managed objects. The agent process performs network management operations such as setting configuration parameters and current operational statistics for a router on a given segment. The managed objects include workstations, servers, wiring hubs, communication circuits, and so on. Associated with the managed objects are attributes, which may be statically defined (such as the speed of the interface), dynamic (such as entries in a routing table), or require ongoing measurement (such as the number of packets transmitted without errors in a given time period).

A database of network management information, called the management information base (MIB), is associated with both the manager and the managed system. Just as a numerical database has a structure for storing and retrieving data, a MIB has a defined organization. This logical organization is called the structure of management information (SMI). The SMI is organized in a tree structure, beginning at the root, with branches that organize the managed objects by logical categories. The MIB represents the managed objects as leaves on the branches.

The network management protocol provides a way for the manager, the managed objects, and their agents to communicate. To structure the communication process, the protocol defines specific messages, referred to as commands, responses, and notifications. The manager uses these messages to request specific management information, and the agent uses them to respond. The building blocks of the messages are called protocol data units (PDUs). For example, a manager sends a GetRequest PDU to retrieve information, and the agent responds with a GetResponse PDU.

How does the manager/agent model relate to the network you need to manage? As you can see in Figure 1-5, a console, such as a SPARC station from Sun Microsystems, Inc., typically performs the network manager functions. The devices on the internetwork, such as routers and host computers, contain network management agents. MIBs are associated with both the manager and agents, but the router’s MIB and the host’s MIB are unlikely to be the same for two reasons. First, these devices usually come from different manufacturers who have implemented network management functions in different, but complementary, ways. Second, routers and hosts perform different internetworking functions and may not need to store the same information. For example, the host may not require routing tables, and thus won’t need to store routing table–related parameters such as the next hop to a particular destination in its MIB. Conversely, a router’s MIB wouldn’t contain a statistic such as CPU utilization that may be significant to a host.


Figure 1-5.  Network manager/agent realization

A protocol such as SNMP allows the manager and the agents to communicate. This protocol provides the structure for commands from the manager, notifies the manager of significant events from the agent, and responds to either the manager or the agent.

Before examining systems from specific vendors, it is useful to look at the various network management implementations. These include the network management system for the International Standards Organization’s (ISO) Open Systems Interconnection (OSI) model (examined in Section 1.5), the IEEE network management architecture (Section 1.6), the Internet Network Management Framework (Section 1.7), SNMP (Section 1.8), and Web-based management (Section 1.10).


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