Snmp Configuration; Introduction To Snmp - Planet XGS3-42000R User Manual

4.4 SNMP Configuration

4.4.1 Introduction to SNMP

SNMP (Simple Network Management Protocol) is a standard net work management protocol widely used in
computer network management. SNMP is an evolving protocol. SNMP v1 [RFC1157] is the first version of
SNMP which is adapted by vast numbers of manufacturers for its simplicity and easy implementation; SNMP
v2c is an enhanced version of SNMP v1, which supports layered net work management; SNMP v3
strengthens the security by adding USM (User-ba sed Security Mode) and VACM (View-based Access
Control Model).
SNMP protocol provides a simple way of exchange net work management information between two points in
the network. SNMP employs a polling mechanism of message query, and transmits messages through UDP
(a connectionless transport layer protocol). Therefore it is well supported by the existing computer networks.
SNMP protoc ol employs a station-agent mode. There are two parts in this structure: NMS (Network
Management Station) and Agent. NMS is the workstation on which SNMP client program is running. It is the
core on the S NMP network management. Agent is the server software runs on the devices which need to be
managed. NMS manages all the managed objects through Agents. The switch supports Agent function.
The communication between NMS and A gent functions in Client/Server mode by exchanging standard
messages. NMS sends request and the Agent responds. There are seven types of SNMP message:

Get-Request

Get-Response

Get-Next-Request

Get-Bulk-Request

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 net work device ports are on Up/Down status or the net work 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 trans fer security by well-designed encryption and authentication. USM encry pts 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 us ed 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.
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