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v
SNMP
consists
of three key components: managed devices, agents, and networkmanagement systems
(NMSs).
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A
managed device is a node that has an SNMP agent and resides on a managed
network. These devices can be routers and access server, switches and bridges,
hubs, computer hosts, or printers.
v
An
agent is a software module residing within a device. This agent translates
information into a compatible format with SNMP.
v
An
NMS runs monitoring applications. They provide the bulk of processing and
memory resources required for network management.
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The
SNMP manager provides the interface between the human network manager and the management
system.
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The
SNMP agent provides the interface between the manager and the physical
device(s) being managed.
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The
SNMP manager and agent use an SNMP Management Information Base (MIB) and
a relatively small set of commands to exchange information.
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The
SNMP MIB is organized in a tree structure with individual variables,
such as point status or description, being represented as leaves on the
branches.
Figure:
- SNMP-Managed Configuration.
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A
long numeric tag or object identifier (OID) is used to distinguish each
variable uniquely in the MIB and in SNMP messages.
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SNMP
uses five basic messages (GET, GET-NEXT, GET-RESPONSE, SET, and TRAP) to
communicate between the SNMP manager and the SNMP agent.
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The
GET and GET-NEXT messages allow the manager to request information for a specific
variable.
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The
agent, upon receiving a GET or GET-NEXT message, will issue a GET-RESPONSE message
to the SNMP manager with either the information requested or an error indication
as to why the request cannot be processed.
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A
SET message allows the SNMP manager to request a change be made to the value of
a specific variable in the case of an alarm remote that will operate a relay.
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The
SNMP agent will then respond with a GET-RESPONSE message indicating the change
has been made or an error indication as to why the change cannot be made.
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The
SNMP TRAP message allows the agent to spontaneously inform the SNMP
manager of an "important" event.
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