Knowledge about SNMP and SNMP Packets

An SNMP packet consists of three parts: version field), region-specific community field) and SNMP protocol data unit field (SNMP protocol data unit field). The packet length is not fixed.

The SNMP protocol also defines the SNMP message stream when the above three SNMP commands are executed, but it does not define other device management proxy SNMP commands, operations that can be applied to MIB Data Objects include the Set and Get commands, which target the values of data objects.

For example, the SNMP protocol does not define a reboot restart) SNMP command. However, the management agent software associates the MIB Data Object with the internal SNMP command of the device, in this way, some special command operations can be implemented. If you want to restart a device, the management system will set the value of a restart-related MIB Data Object to 1 ).

This will trigger the management agent to execute the SNMP command to restart the device, and reset the MIB Data Object to the original state.

Version domain: this domain is used to describe which version of SNMP protocol is used now. Currently, version 1 is the most widely used SNMP protocol.
 
Partition: partition community) is a basic security mechanism used for identity authentication when the SNMP Network Administrator accesses the SNMP Management proxy.

Partition name Community name) is the password for managing the proxy. The Administrator is allowed to access data objects only when the network administrator knows the password for the network proxy. If you use the Configuration Management proxy to execute the Trap Command, when the network administrator queries the management proxy with an incorrect partition name, the system sends an autenticationFailure trap SNMP message.

Protocol Data Unit domain: There are five types of PDUS in SNMPv1, some of which are SNMP packet Request requests, and some are Response responses ). These include GetRequest, GetNextRequest, SetRequest, GetResponse, and Trap. SNMPv2 adds two types of PDU: GetBulkRequest and InformRequest.

The SNMP administrator uses GetRequest to retrieve information from the network device with the SNMP proxy. The SNMP proxy responds to the GetRequest message with the GetResponse message. There is a lot of information that can be exchanged, such as the system name, the time when the system runs normally after it is started, and the number of network interfaces in the system. GetRequest and GetNextRequest can be used together to obtain objects in a table.

GetRequest retrieves a specific object, while GetNextRequest is the next object in the request table. You can use SetRequest to remotely configure parameters in a device. Set-Request allows you to Set the device name, disable a port, or clear items in an address resolution table. Trap is an SNMP Trap. It is a non-request message sent by the SNMP agent to the management site. Here is an introduction to SNMP packets.