SNR S2989G-48TX-DC — обзор протокола SNMP: управление сетью и безопасность [39/553]
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SNR S2989G-48TX-DC — обзор протокола SNMP: управление сетью и безопасность [39/553]

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SNR S2989G-48TX-POE Руководство по настройке онлайн [39/553] 747269
S2989G-24TX Operation Manual
Chapter
1
Basic
Management
Configuration
1-24
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 network management; SNMP v3 strengthens
the security by adding USM (User-based Security Mode) and VACM (View-based Access
Control Model).
SNMP protocol provides a simple way of exchange network 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 protocol 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 SNMP 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 Agent 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 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.

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