Snmp Manager And Agent Communication - Cisco ACE-4710-K9 Administration Manual

SNMP Overview

SNMP Manager and Agent Communication

Cisco 4700 Series Application Control Engine Appliance Administration Guide
8-4
The SNMP manager and the agent can communicate in several ways. The Protocol
Data Unit (PDU) is the message format that SNMP managers and agents use to
send and receive information.
The SNMP manager can do the following:
•
Retrieve a value (a get operation) from an agent. The SNMP manager
–
requests information from the agent, such as the number of users logged
on to the agent device, or the status of a critical process on that device.
The agent gets the value of the requested MIB object and sends the value
back to the manager (a get-response operation). The variable binding
(varbind) is a list of MIB objects that allows a request recipient to see
what the originator wants to know. Variable bindings can be thought of
as OID=value pairs that make it easy for the NMS to identify the
information that it needs when the recipient fills the request and sends
back a response.
Retrieve the value immediately after the variable that you name (a
–
get-next operation). A get-next operation retrieves a group of values
from a MIB by issuing a sequence of commands. By performing a
get-next operation, you do not need to know the exact MIB object
instance you are looking for; the SNMP manager takes the variable that
you name and then uses a sequential search to find the desired variables.
Retrieve a number of values (a get-bulk operation). The get-bulk
–
operation retrieves large blocks of data, such as multiple rows in a table,
which would otherwise require the transmission of many small blocks of
data.The SNMP manager performs a number of get-next operations that
you specify.
An agent can send an unsolicited message to the SNMP manager at any time
•
if a significant, predetermined event takes place on the agent. This message
is called an event notification. SNMP event notifications (traps or inform
requests) are included in many MIBs and help to alleviate the need for the
NMS to frequently poll (gather information through a get operation) the
managed devices. For details on MIB objects and SNMP notifications
supported by the ACE, see the
Chapter 8
"Supported MIBs and Notifications"
Configuring SNMP
section.
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