Developers guide

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D. SNMP overview
D.1. Architecture
The Simple Network Management Protocol (SNMP), is a standard designed to allow the remote
management of devices across a network. This standard, defined in [ 18 ], facilitates
communication between an SNMP Agent (managed device), and a Network Management
Station (NMS).
Device management is achieved by a simple system of getting and setting of attributes on the
remote device. Attributes, or Object Identifiers are defined in the agent’s Management
Information Base (MIB), a repository containing definitions of all the OID’s within an agent.
Objects within an agent belong to a particular SNMP Community
i
. The community name, known
only to the system administrator, is used to authenticate messages.
Communication is achieved via SNMP Messages, as shown in Figure D-2. Sent as UDP packets,
they contain three pieces of information:
1. SNMP version number. Included to guarantee the correct dissection of packets in an
environment where multiple SNMP agents, supporting different versions, exist.
2. Community name.
3. One or more Protocol Data Units (PDU’s). A PDU typically contains a list of OID’s and their
corresponding values.
SNMP Version
PDU
Community
PDU
PDU’s
Figure D-1 SNMP
message
There are three kinds of SNMP messages:
• Request
o GET, Read information from the SNMP Agent corresponding to an attribute of the
managed device.
o GET NEXT, Do a get on the next attribute in the tree. This is used to traverse each
OID within the SNMP agent, otherwise known as an SNMP-walk.
o SET, Set the value of an attribute of a managed device.
• Response
i
Typically, all objects within an agent will belong to the same community,