HP Cisco Catalyst Blade Switch 3020 Cisco Catalyst Blade Switch 3020 for HP So - Page 476

Understanding SNMP Chapter 25 Configuring 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 Using SNMP to Access MIB Variables An example of an NMS is the CiscoWorksnetwork 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 25-1, 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 25-1 NMS SNMP Network 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." 25-4 Cisco Catalyst Blade Switch 3020 for HP Software Configuration Guide OL-8915-01