Cisco MCS-7825-H3-IPC1, Руководство по обслуживанию

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4-4
Cisco Unified Communications Manager Managed Services Guide
OL-22523-01
Chapter 4 Simple Network Management Protocol
SNMP Community Strings and Users
SNMP Community Strings and Users
Although SNMP community strings provide no security, the strings authenticate access to MIB objects
and function as embedded passwords. You configure SNMP community strings for SNMP v1 and v2c
only.
SNMP v3 does not use community strings. It uses SNMP users that serve the same purpose as
community strings but provide security because encryption or authentication is configured.
No default community string or user exists.
SNMP and Cisco MIBs
You can access the Cisco MIB variables by using SNMP which facilitates the exchange of management
information between network devices. The SNMP system comprises three parts: SNMP manager, SNMP
agent, and MIB.
Instead of defining a large set of commands, SNMP places all operations in a get-request ,
get-next-request , get-bulk-request , and set-request format. For example, an SNMP manager can get a
value from an SNMP agent or store a value in that SNMP agent. The SNMP manager can comprise part
of a network management system (NMS), and the SNMP agent can reside on a networking device such
as a router. You can compile the Cisco MIB with your network management software. If SNMP is
configured on a router, the SNMP agent can respond to MIB-related queries that are being sent by the
NMS.
The NMS uses the Cisco MIB variables to set device variables and to poll devices on the internetwork
for specific information. The results of a poll can get graphed and analyzed to help you troubleshoot
internetwork problems, increase network performance, verify the configuration of devices, monitor
traffic loads, and more.
The SNMP agent gathers data from the MIB, which provides the repository for information about device
parameters and network data. The SNMP agent also can send traps (notifications) of certain events, to
the SNMP manager. The Cisco host
//ftp.cisco.com makes available the Cisco trap file, “mib.traps,”
which documents the format of Cisco traps.
The SNMP manager uses information in the MIB to perform the operations as described:
Operation Description
get-request Retrieve a value from a specific variable.
get-next-request Retrieve the value following the named variable. Often used to retrieve
variables from within a table. 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 the MIB.
get-response The reply to a get-request, get-next-request, get-bulk-request, and set-request
sent by an NMS.
get-bulk-request Similar to get-next-request, but fills the get-response with up to
max-repetition number of get-next interactions.
set-request Store a value in a specific variable.
traps An unsolicited message sent by an SNMP agent to an SNMP manager
indicating that some event has occurred.