Management Information Base (Mib); Snmp Agent Overview; System Configuration - HP StorageWorks XP20000/XP24000 - Disk Array Reference Manual

An SNMP manager monitors the devices, which are referred to as managed nodes. The primary types
of interaction between the SNMP manager and an SNMP agent are polling and trap. Typically, the
SNMP manager polls the SNMP agents on a periodic basis, to determine whether the device is
operating normally. If an abnormal event occurs, the SNMP Agent can report the condition without
a request from the manager, by using a message called trap.
When an SNMP Manager polls the agent, the following dialog takes place:
An SNMP manager sends a request packet to an SNMP agent, which requests data regarding
the status of managed node.
The SNMP agent sends a response packet back to the SNMP manager.
SNMP uses the TCP/IP User Datagram Protocol (UDP). If the SNMP agent does not respond
within a specified time period, the SNMP manager re-sends the request packet. That time period
is set by the system administrator, taking into account the network traffic and operation policy.
If an SNMP agent again does not respond to the re-sent packet, the SNMP manager assumes that
an error has occurred. Depending on the times set for polling and response, this can take several
seconds.
If an SNMP agent detects an abnormal event, it sends a trap to the SNMP manager. However, if a
trap is dropped in transmission, the SNMP manager does not know that it was sent. For this reason,
you should use both polling and traps to determine whether an abnormal event has occurred.

Management Information Base (MIB)

Each managed device has certain types of information, including the configuration information, the
status information for device, and statistical, which is known collectively as a Management Information
Base (MIB). Each parameter is called a managed object, and it consists of the parameter name, one
or more parameter(s), and a group of operations that can be executed with the object. The MIB defines
the type of information that can be obtained from a managed device, and the device settings that
can be controlled from a management system.

SNMP Agent Overview

System Configuration

The SNMP agent for the HP storage system is on the service processor (SVP), which is the computer
within the storage array that manages the storage system. The storage system has an exclusive LAN
for communications between a disk controller and a service processor, and a separate LAN for SNMP.
The configuration of each Network Management Station is determined by the type of SNMP Manager.
The following figure illustrates the SNMP environment.
8 Overview of SNMP