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322 CHAPTER 11: SYSTEM MANAGEMENT
SNMP The Simple Network Management Protocol (SNMP) is used for transmitting
management information between any two nodes. In this way, network
administrators can easily search and modify the information on any node on the
network. They can also locate faults promptly and implement the fault diagnosis,
capacity planning, and report generating. SNMP adopts the polling mechanism
and provides the most basic function set. It is most applicable to the small-sized,
fast-speed, and low-cost environment. It only requires the unverified transport
layer protocol UDP, and is widely supported by many other products.
In terms of structure, SNMP can be divided into two parts, NMS and Agent. NMS
(Network Management Station) is the workstation for running the client program.
At present, the commonly used NM platforms include Sun NetManager and IBM
NetView. The agent is the server software operated on network devices. NMS can
send GetRequest, GetNextRequest, and SetRequest messages to the agent. Upon
receiving the requests from the NMS, the agent will perform a read or write
operation according to the message types, and generate and return the response
message to NMS. On the other hand, the agent will send a trap message on its
own initiative to NMS to report events whenever the device encounters any
abnormalities.
Configuring SNMP is described in the following sections:
■ SNMP Versions and Supported MIB
■ Configuring SNMP
SNMP Versions and
Supported MIB
To uniquely identify the management variables of a device in SNMP messages,
SNMP adopts the hierarchical naming scheme to identify the managed objects. It
is like a tree. A tree node represents a managed object, as shown in the figure
below. Thus the object can be identified with the unique path starting from the
root.
Figure 4 Architecture of the MIB Tree
The MIB (Management Information Base) is used to describe the hierarchical
architecture of the tree, and is the set defined by the standard variables of the
monitored network device. In the above figure, the managed object B can be
uniquely specified by a string of numbers {1.2.1.1}. The number string is the
Object Identifier of the managed object.
1
1
2
2
2
65
1
1
A
B