H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 122)

18-2
SNMP provides the following four basic operations:
Get operation: NMS gets the value of a certain variable of the agent through this operation.
Set operation: NMS can reconfigure the value of one or more objects in the agent MIB
(Management Information Base) by means of this operation.
Trap operation: The agent sends traps to the NMS through this operation.
Inform operation: The 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 uses community name for authentication. Community name defines the relationship
between an SNMP NMS and an SNMP agent. SNMP packets with community names that do not
pass the authentication on the device are simply discarded. A community name plays a similar role
as a key word and can be used to control access from NMS to the agent.
SNMPv2c uses community name for authentication. 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 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 agents, preventing the packets from being
intercepted. USM ensures a more secure communication between SNMP NMS and SNMP agent
by authentication with privacy.
Successful interaction between NMS and agents requires consistency of SNMP versions configured on
them. You can configure multiple SNMP versions for an agent to interact with different NMSs.
MIB Overview
MIB
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 the hierarchy
of the objects and a set of characteristics associated with the managed objects, such as the object
identifier (OID), access right and data type. Each agent has its own MIB. NMS can read or write the
managed objects in the MIB. The relationship between an NMS, agent and MIB is shown in Figure 18-1 .
Figure 18-1 Relationship between NMS, agent and MIB
Subtree OID
MIB stores data using a tree structure. A node of the tree is a managed object and can be uniquely
identified by a path starting from the root node. As illustrated in Figure 18-2 , the managed object A can