C H A P T E R 4 Simple Network Management Protocol; Snmp Versioning - Cisco MCS-7825-H3-IPC1 Service Manual

SNMP Versioning

The SNMP agent gathers data from the MIB, which is 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
get-request
get-next-request
get-response
get-bulk-request
set-request
traps
SNMP Versioning
Three versions of SNMP exist: version 1 (SNMPv1), version 2 (SNMPv2), and version 3 (SNMPv3).
SNMPv1 represents the initial implementation of SNMP that functions within the specifications of the
Structure of Management Information (SMI) and operates over protocols, such as User Datagram
Protocol (UDP) and IP.
The SNMPv1 SMI defines highly structured MIB tables that are used to group objects that contain
multiple variables. Tables contain zero or more rows, which are indexed, so SNMP can retrieve or alter
an entire row with a supported command.
With SNMPv1, the NMS issues a request, and managed devices return responses. Agents use the Trap
operation to asynchronously inform the NMS of a significant event.
As with SNMPv1, SNMPv2c functions within the specifications of SMI. MIB modules contain
definitions of interrelated managed objects. Be aware that the operations that are used in SNMPv1 are
similar to those that are used in SNMPv2. The SNMPv2 trap operation, for example, serves the same
function as that used in SNMPv1, but it uses a different message format and replaces the SNMPv1 trap.
The Inform operation in SNMPv2c enables one NMS to send trap information to another NMS and to
receive a response from the NMS.
SNMPv3 provides the following security features:
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Description
Retrieve a value from a specific variable.
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 gets performed to
find the needed variable from within the MIB.
Reply to a get-request, get-next-request, get-bulk-request, and set-request that
an NMS sent.
Fills the get-response with up to max-repetition number of get-next
interactions, similar to get-next-request.
Store a value in a specific variable.
Sent by an SNMP agent to an SNMP manager to indicate that some event
occurred.
Authentication—Verifying that the request comes from a genuine source.
Privacy—Encrypting data.
Authorization—Verifying that the user allows the requested operation.
Access control—Verifying that the user has access to the objects that are requested.
Chapter 4 Simple Network Management Protocol
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