932 CHAPTER 75: SNMP CONFIGURATION
■ Get operation: NMS gets the value of a certain variable of Agent through this
operation.
■ 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.
■ Trap operation: Agent sends Traps to the NMS through this operation.
■ 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.
■ 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.
■ 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.
■ 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 272.
Figure 272 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 B can be uniquely identified by a
AgentNMS
MIB
Get/Set requests
Get /Set responses
and Traps
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