Manual

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Москва, Новозаводская ул., 18, стр. 1

 Set-Request

 Trap

 Inform-Request

NMS sends queries to the Agent with Get-Request, Get-Next-Request, Get-Bulk-Request and

Set-Request messages; and the Agent, upon receiving the requests, replies with Get-

Response message. On some special situations, like network device ports are on Up/Down

status or the network topology changes, Agents can send Trap messages to NMS to inform the

abnormal events. Besides, NMS can also be set to alert to some abnormal events by enabling

RMON function. When alert events are triggered, Agents will send Trap messages or log the

event according to the settings. Inform-Request is mainly used for inter-NMS communication in

the layered network management.

USM ensures the transfer security by well-designed encryption and authentication. USM

encrypts the messages according to the user typed password. This mechanism ensures that

the messages can’t be viewed on transmission. And USM authentication ensures that the

messages can’t be changed on transmission. USM employs DES-CBC cryptography. And

HMAC-MD5 and HMAC-SHA are used for authentication.

VACM is used to classify the users’ access permission. It puts the users with the same access

permission in the same group. Users can’t conduct the operation which is not authorized.

2.4.2 Introduction to MIB

The network management information accessed by NMS is well defined and organized in a

Management Information Base (MIB). MIB is pre-defined information which can be accessed

by network management protocols. It is in layered and structured form. The pre-defined

management information can be obtained from monitored network devices. ISO ASN.1 defines

a tree structure for MID. Each MIB organizes all the available information with this tree

structure. And each node on this tree contains an OID (Object Identifier) and a brief description

about the node. OID is a set of integers divided by periods. It identifies the node and can be

used to locate the node in a MID tree structure, shown in the figure below: