Cisco Systems 3750E manual Snmp Agent Functions, Using Snmp to Access MIB Variables, 33-4

Chapter 33 Configuring SNMP

Understanding SNMP

SNMP Agent Functions

The SNMP agent responds to SNMP manager requests as follows:

•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.

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:

•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

•When a cluster is created, the command switch manages the exchange of messages among member switches and the SNMP application. The Network Assistant software appends the member switch number (@esN, where N is the switch number) to the first configured RW and RO community strings on the command switch and propagates them to the member switches. For more information, see Chapter 6, “Clustering Switches” and see Getting Started with Cisco Network Assistant, available on Cisco.com.

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.

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

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