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Understanding SNMP
SNMP Agent Functions
The SNMP agent responds to SNMP manager requests as follows:
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The SNMP agent also sends unsolicited trap messages to notify an NMS that a significant event has
occurred on the agent. Examples of trap conditions include, but are not limited to, when a port or module
goes up or down, when spanning-tree topology changes occur, and when authentication failures occur.
SNMP Community Strings
SNMP community strings authenticate access to MIB objects and function as embedded passwords. In
order for the NMS to access the switch, the community string definitions on the NMS must match at least
one of the three community string definitions on the switch.
A community string can have one of these attributes:
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•
Using SNMP to Access MIB Variables
An example of an NMS is the CiscoWorks network management software. CiscoWorks 2000 software
uses the switch MIB variables to set device variables and to poll devices on the network for specific
information. The results of a poll can be displayed as a graph and analyzed to troubleshoot
internetworking problems, increase network performance, verify the configuration of devices, monitor
traffic loads, and more.
As shown in
notification of certain events, to the SNMP manager, which receives and processes the traps. Traps alert
the SNMP manager to a condition on the network such as improper user authentication, restarts, link
status (up or down), MAC address tracking, and so forth. The SNMP agent also responds to MIB-related
queries sent by the SNMP manager in get-request, get-next-request, and set-request format.
Figure 33-1
SNMP Manager
For information on supported MIBs and how to access them, see
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
33-4
Get a MIB variable—The SNMP agent begins this function in response to a request from the NMS.
The agent retrieves the value of the requested MIB variable and responds to the NMS with that value.
Set a MIB variable—The SNMP agent begins this function in response to a message from the NMS.
The SNMP agent changes the value of the MIB variable to the value requested by the NMS.
Read-only (RO)—Gives read access to authorized management stations to all objects in the MIB
except the community strings, but does not allow write access
Read-write (RW)—Gives read and write access to authorized management stations to all objects in
the MIB, but does not allow access to the community strings
Figure
33-1, the SNMP agent gathers data from the MIB. The agent can send traps, or
SNMP Network
Get-request, Get-next-request,
NMS
Get-bulk, Set-request
Get-response, traps
Chapter 33
Network device
MIB
SNMP Agent
Appendix A, "Supported MIBs."
Configuring SNMP
OL-12247-04
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