SNMPv2: Simple Network Management Protocol version 2nd

(SNMPv2: Simple Network Management Protocol V2)

 

SNMP is a standard protocol used to manage network nodes (servers, workstations, routers, switches, and hubs) in an IP network. It is an application layer protocol. SNMP enables network administrators to manage network performance, discover and solve network problems, and plan network growth. The Network Management System receives random messages (and event reports) through SNMP to learn about network problems. Currently, SNMP has three versions: SNMPv1, SNMPv2, and SNMPv3. This topic describes information about SNMPv2. SNMPv2 evolved from SNMPv1. The get, getnext, and set operations in SNMPv1 are also applicable to SNMPv2, but SNMPv2 adds and enhances relevant protocol operations. For example, the trap operation in SNMPv2 not only has the same trap function in SNMPv1, but also uses a different message format, which is used to replace the trap in SNMPv1. Two new operations are also set in SNMPv2, namely get bulk and inform. NMS can effectively obtain large data blocks through the get bulk operation, such as multiple rows in the object list. GETBULK returns a response message containing as much request data as possible. The inform operation enables one NMS to send traps to another NMs and receive replies. In SNMPv2, if the SNMP Agent replying to the get bulk operation cannot provide all the variable values in the request table, the SNMP agent only provides partial results. For more information about SNMP, SNMPv1, and SNMPv3, see the relevant section.

 

Protocol Structure

 

SNMP is an application.ProgramProtocol, encapsulated in UDP. Common SNMP information formats of different versions are as follows:

 

Version

Community

PDU

 

Version: SNMP version number. The manager and agent must use the same version of SNMP. You need to delete information with different version numbers without further processing them. Community: group name, used to authenticate the manager before accessing the proxy. PDU (Protocol Data Unit): The PDU types and formats in SNMPv1, V2, and V3 are described in the corresponding file.

In SNMPv2, get, getnext, inform, response, set, and trap PDUS have the following formats:

 

PDU type

Request ID

Error status

Error Index

Object 1, value 1

Object 2, value 2

...

 

PDU type: Identify the PDU type transmitted (get, getnext, inform, response, set, or trap ). Request ID: Connection SNMP request and response. Error status: indicates an error and error type. This field can be set only for the response operation. For other operations, this field is set to 0. Error index: connects an error and a special object instance. This field can be set only for the response operation. For other operations, this field is set to 0. Variable bindings: Used as the data field of the SNMPv2 PDU (value 1, value 2 ...). Each variable is bound to a special object instance under the current value (except for the get and getnext requests, which are ignored in the value.

 

The SNMPv2 getbulk pdu format is as follows:

 

PDU type

Request ID

Non Repeaters

Max repetitions

OBJ 1, Val 1

OBJ 1, Val 1

...

 

PDU type: identifies a PDU as a GETBULK operation. Request ID: Connection SNMP request and response. Non Repeaters: Specifies the instance number of the object in the variable binding field, and searches for it multiple times from the request. This field is used when the instance is a scalar object with only one variable. Max repetitions: defines the maximum number of times a variable is retrieved except the variable specified by the non repeaters field. Variable bindings: Used as the SNMPv2 PDU data field (Object 1, object 2 ......). Each variable is bound to a special object instance under the current value (except for the get and getnext requests, which are ignored in the value.