FW 05.01.00 and SW 07.01.00 HP StorageWorks SNMP Reference for Directors and Edge Switches Reference Guide (AA-RQ7BD-TE, June 2003)

Introduction to SNMP
18 SNMP Reference for Directors and Edge Switches
Why Variables Exist In a Managed Device
Variables are the means by which a Director or Edge Switch (and other devices)
keep track of their performance, control their own performance, and provide
access to their performance for network managers. A simple example of a
variable’s use is to set a port offline and turn the port back on. Some variables just
hold values that indicate status (for example error counts). SNMP allows the
network managers to have access to some of the same variables for network
management.
For purposes of the following explanation, an object is a data variable that
represents an attribute of a managed device.
How SNMP Changes Variables (Objects) in a Managed Device
An agent is the entity that interfaces to the actual object being managed
(Figure 2). The agent understands the language of SNMP and translates between
the manager and the object. Objects may be retrieved and/or modified by the
manager, and it is the agent’s job to return the requested object’s value.
Within the agent is at least one, maybe several, collections of definitions called
Management Information Bases (MIBs). When an agent supports a standard MIB,
it agrees to provide and make available the variables listed in the MIB.
A MIB is a hierarchical tree of groups and variables. Operators at a network
management station enter a command with supported groups and variables from
the MIB.