H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 470)

52-2
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NMS manages an SNMP enabled network, whereas Agent is the managed network device. They
exchange management information through the SNMP protocol.
SNMP provides the following four basic operations:
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Get operation: NMS gets the value of a certain variable of Agent through this operation.
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Set operation: NMS can reconfigure certain values in the Agent MIB (Management Information
Base) to make the Agent perform certain tasks by means of this operation.
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Trap operation: Agent sends Traps to the NMS through this operation.
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Inform operation: NMS sends Traps to other NMSs through this operation.
SNMP Protocol Version
Currently, SNMP agents support SNMPv3 and are compatible with SNMPv1 and SNMPv2c.
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SNMPv1 authenticates by means of community name, which defines the relationship between an
SNMP NMS and an SNMP Agent. SNMP packets with community names that did not pass the
authentication on the device will simply be discarded. A community name performs a similar role as
a key word and can be used to regulate access from NMS to Agent.
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SNMPv2c authenticates by means of community name. Compatible with SNMPv1, it extends the
functions of SNMPv1. SNMPv2c provides more operation modes such as GetBulk and
InformRequest; it supports more data types such as Counter64 and Counter32; and it provides
various error codes, thus being able to distinguish errors in more detail.
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SNMPv3 offers an authentication that is implemented with a User-Based Security Model (USM).
You can set the authentication and privacy functions. The former is used to authenticate the validity
of the sending end of the authentication packets, preventing access of illegal users; the latter is
used to encrypt packets between the NMS and Agent, preventing the packets from being
intercepted. USM ensures a more secure communication between SNMP NMS and SNMP Agent
by authentication with privacy, authentication without privacy, or no authentication no privacy.
Successful interaction between NMS and Agent requires consistency of SNMP versions configured on
them. You can configure multiple SNMP versions for an Agent to interact with different NMSs.
MIB Overview
Any managed resource can be identified as an object, which is known as the managed object.
Management Information Base (MIB) is a collection of all the managed objects. It defines a set of
characteristics associated with the managed objects, such as the object identifier (OID), access right
and data type of the objects. Each Agent has its own MIB. NMS can read or write the managed objects
in the MIB. The relationship between NMS, Agent and MIB is shown in
Figure 52-1 .
Figure 52-1 Relationship between NMS, Agent and MIB
MIB stores data using a tree structure. The node of the tree is the managed object and can be uniquely
identified by a path starting from the root node. As illustrated in the following figure, the managed object