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Configuring SNMP
Information About 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.
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 73 on page 531, 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.
1. With this operation, an SNMP manager does not need to know the exact variable name. A sequential search is performed
to find the needed variable from within a table.
2. The get-bulk command only works with SNMPv2 or later.
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