Information Technology Reference
In-Depth Information
The NMS manager uses the Get operation to retrieve the value-specific MIB variable from
an agent. The GetNext operation is used to retrieve the next object instance in a table or
list within an agent. The Get Response contains the value of the requested variable.
The NMS manager uses the Set operation to set values of the object instance within an
agent. For example, the Set operation can be used to set an IP address on an interface or
to bring an interface up or down. Agents use the Trap operation to inform the NMS man-
ager of a significant alarm event. For example, a trap is generated when a WAN circuit
goes down.
SNMPv2
SNMPv2 is an evolution of the initial SNMPv1 and is defined in RFCs 1901 and 1902.
SNMPv2 offers improvements to SNMPv1, including additional protocol operations. The
Get, GetNext, and Set operations used in SNMPv1 are exactly the same as those used in
SNMPv1. The SNMP Trap operation serves the same function as in SNMPv1, but it uses a
different message format.
SNMPv2 defines two new protocol operations:
GetBulk:
Reduces repetitive requests for MIB variables
■
Inform request:
Alerts an SNMP manager of specific conditions with confirmation
■
The NMS manager uses the GetBulk operation to retrieve large blocks of data, such as
multiple rows in a table. This is more efficient than repeating GetNext commands. If the
agent responding to the GetBulk operation cannot provide values for all the variables in a
list, it provides partial results. The Inform operation allows one NMS manager to send trap
information to other NMS managers and to receive information. Another improvement is
that data type values can be 64 bits.
Ta ble 1 5 - 3 summarizes SNMP message types.
Ta b l e 1 5 - 3
SNMP Message Types
SNMP Message
Description
Get request
Retrieves the value of a specific MIB variable
GetNext request
Retrieves the next issuance of the MIB variable
Get response
Contains the values of the requested variable
Set request
Modifies the value of a MIB variable
Trap
Tran s mits an un s olic ited alar m condit ion
GetBulk
Reduces repetitive requests for MIB variables
Inform request
Alerts an SNMP manager of specific conditions with confirmation
SNMPv3
SNMPv3 was developed to correct several deficiencies in the earlier versions of
security being a primary reason. SNMPv3 is defined in RFCs 3410 through 3415. SNMPv3
