Amer Networks SS2R48G4i V2 - Manual (Page 59)

SS2R24G4i/SS2R48G4i
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5.4 SNMP Configuration
5.4.1 Introduction To SNMP
SNMP (Simple Network Management Protocol) is a standard network 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 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
z Get-Request
z Get-Response
z Get-Next-Request
z Get-Bulk-Request
z Set-Request
z Trap
z 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.