SNMP definition

SNMP stands for Simple Network Management Protocol, and it is a popular network protocol meant for IP networks and works with most network devices. It is used mainly for managing and monitoring the existing devices in a network. 

It is also an extension of the TCP/IP protocol and helps sysadmins or network administrators to remotely configure and get information from devices such as routers, servers, etc. 

SNMP is an application layer protocol, or OSI layer 7, and it works on Client/Server model. SNMP specifically uses UDP ports 161, which is the manager, and 162 being the agent. The most popular versions of SNMP are SNMPv2c and SNMPv3.

SNMP components explained

SNMP has five major components:

• SNMP Manager

The SNMP manager is also referred to as a network management station (NMS). This software application monitors the network and communicates with the network devices through SNMP agents. It is placed on a network host, which is either a computer or directly on the network. 

The manager sends queries to agents to get information from them, also configuring their settings and receiving alerts about any events that pop up.

• Devices

Commonly managed devices are routers, switches, servers, and even printers. In some cases, SNMP monitors firewalls, workstations, apps, etc. 

• SNMP agent

An agent is a program that runs on a device such as a router or a switch, and it collects and reports data about that device to its SNMP manager. It also maintains a database (MIB), and it can extend the workbase to subagents. 

In a printer, values such as printer status, toner level, etc., could be the data that agents use. 

There’s also the possibility of using a master agent that manages its subagents. The master agent is the central hub for the SNMP manager, and it handles the communication with its multiple subagents. It acts like an intermediary between the SNMP manager and those subagents. The manager is not aware of the existence of the subagents and only interacts with the master agent. 

• Management information base (MIB)

MIBs refer to the hierarchical database that has the managed objects, traps, and other relevant information from a network device. It acts like a bridge between the SNMP managers and their agents so they can exchange data about said devices. 

A good example of the stored data about a printer is the name of it, the different cartridges it uses, and the number of pages it printed during its use. 

• SNMP OID

OID refers to Object Identifiers and represents a unique address (numeric or alphanumeric) that is used to identify objects in an MBI. It consists of two parts, the data type and the operations that are available. For example, the printer’s name, its toner level, and its status could have an OID.

How does it work? 

The way it works: an agent runs on a device (take the printer as an example), which then collects information about it. The SNMP manager then sends requests for specific information that is defined in the MIB (Management information base). 

For example, the manager might ask about the printer’s toner level, and it’ll pick up on the OID of the toner level, and the printer’s agent will respond with the current percentage. This allows admins to monitor and manage printers remotely. 

SNMP ports and trap notifications 

The SNMP port numbers are the set of UDP server ports that are used for the communication between the SNMP managers and their agents:

• The UDP point 161 is used by the SNMP manager to send requests to its agents. 

• The UDP port 162 is used by agents/master agents to send trap notifications to their managers. 

All versions of SNMP use the same ports.

A trap notification is a notification that is sent by a device to the SNMP manager, and it automatically alerts the manager about any events or issues. They’re convenient because the notifications are sent when they’re triggered, so there’s no need for specific requests.

Why is SNMP important?

SNMP is an interface that keeps track of the network’s devices and helps administrators in finding and fixing problems. It also helps by boosting productivity and maintaining the stability of the network. 

From the perspective of network visibility and the control of it, admins can solve any problems that pop up by recognizing and correcting errors before they cause further damage.