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Catalyst 3750 SwitchSoftware Configuration Guide
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Chapter32 Configuring SNMP
Understanding SNMP
SNMP Manager Functions
The SNMP manager uses information in the MIB to perform the operations described in Table32-2.
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.
Table32-2 SNMP Operations
Operation Description
get-request Retrieves a value from a specific variable.
get-next-request Retrieves a value from a variable within a table.1
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.
get-bulk-request2
2. The get-bulk command only works with SNMPv2 or later.
Retrieves large blocks of data, such as multiple rows in a table, that would otherwise require the
transmission of many small blocks of data.
get-response Replies to a get-request, get-next-request, and set-request sent by an NMS.
set-request Stores a value in a specific variable.
trap An unsolicited message sent by an SNMP agent to an SNMP manager when some event has occurred.