Detailed explanation of commands and proxies in Linux SNMP

In the learning of SNMP protocol, we have been constantly explaining the knowledge of Linux SNMP. Next, we will analyze the two parts. The first step is to introduce the SNMP command, and then analyze the SNMP agent. We hope that you can learn important knowledge about Linux SNMP.

SNMP command

The SNMP command is a shortcut for operating SNMP in Linux. Simple Network Management Protocol (SNMP) is a Simple Network Management Protocol. It provides a framework for the Network Management system to manage the underlying Network.

The SNMP Protocol defines the data packet format and information exchange between the network administrator and the management agent. It also controls the MIB Data Objects of the management agent. Therefore, it can be used to process various tasks defined by the management agent. The SNMP protocol is easy to use because it provides three basic SNMP commands for controlling MIB objects.

They are: Set, Get, and Trap:

Set: it is a privileged SNMP command, because it can be used to modify the configuration of the device or control the running status of the device.
 
Get: it is an SNMP command with the highest usage in the SNMP protocol, because this SNMP command is the basic way to obtain management information from network devices.
 
Trap: when the network management system has no clear requirements, the management agent notifies the network management system of some special situations or problems.
 
The SNMP protocol also defines the packet flow 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.

You may have heard about "Linux SNMP management devices", "Linux SNMP-compatible devices", or "Linux SNMP-managed devices. But what exactly are they? How are they different from smart devices?

Simply put, all the above statements mean "a network device that includes the network management proxy ". These also mean that the proxy supports the Linux SNMP protocol for information exchange. As mentioned above, a smart device may not need to use or support the Linux SNMP protocol. So what is a proxy?

SNMP proxy

Management agent) is a special software or firmware. It contains information about a special device and/or the environment where the device is located. When a proxy is installed on a device, the above devices are listed as "managed ". In other words, a proxy is a database.

The data contained in the database varies with the installed device. For example, on a vro, the proxy will contain information about the route selection table, the total number of received and sent packets, and so on. For a bridge, the database may contain information about the number of forwarding packets and the filtering table.

A proxy is a software or firmware that communicates with the network management console. You can perform the following tasks on the "Link" of the console:

◆ The network management workstation can obtain information about the device from the agent.

◆ The network management workstation can modify, add, or delete table items in the proxy, for example, selecting table items for routes in the database maintained by the proxy.

◆ The network management workstation can set a threshold value for a specific self-trap.

◆ Self-traps can be sent to the network management workstation.

Remember that the agent in the managed device does not provide information voluntarily unless there is an event when the threshold is exceeded.

In some accidental circumstances, a specific device may be missing due to system resources, or because the device does not support the transport protocol required by the Linux SNMP agent, but cannot implement a Linux SNMP proxy. Does this mean you cannot monitor this device? This is not the case. In this case, there is no way at all. You can use the trusted proxy agent), which is equivalent to the external device foreign device ).

The trusted proxy does not run on managed external devices, but on another device. The network management workstation first contacts the Trusted agent and points out that the consistency between the Trusted agent and external devices is achieved through some method. Then the delegate translates the protocol commands it receives into the management protocols supported by any external device. In this case, the trusted proxy is called the application gateway ).

If an external device does not support any management protocols, the delegated agent must use some passive methods to monitor the device. For example, a trusted proxy of a ring bridge can monitor its performance and generate self-traps if it detects any congestion errors reported by the bridge.

Fortunately, most Internet devices currently support Linux SNMP management devices, so you can easily use a Linux SNMP to manage devices, such as hubs, bridges, and routers. Some vendors even provide Linux SNMP agents on their NICs.