Cisco 2950G 24 Software Configuration Guide - Page 480

Understanding SNMP Chapter 24 Configuring SNMP 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 • Read-write-all-Gives read and write access to authorized management stations to all objects in the MIB, including the community strings Note When a cluster is created, the command switch manages the exchange of messages among member switches and the SNMP application. The Cluster Management 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." 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 Figure 24-1, the SNMP agent gathers data from the MIB. The agent can send traps, or 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 24-1 SNMP Network NMS Get-request, Get-next-request, Get-bulk, Set-request Network device 43581 SNMP Manager Get-response, traps MIB SNMP Agent For information on supported MIBs and how to access them, see Appendix A, "Supported MIBs." 24-4 Catalyst 2950 Desktop Switch Software Configuration Guide 78-14982-01