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What is SNMP port and how does it work?

Here's a detailed blog about what is SNMP (Simple Network Management Protocol) and how it works.

05 Dec, 22 by Susith Nonis 11 min Read

List of content you will read in this article:

A group of protocols called Simple Network Management Protocol (SNMP) are used for network management and monitoring. It monitors network equipment, including firewalls, bridges, routers, switches, printers, servers, UPS, NAS drives, and more.

This protocol enables information sharing across devices with various hardware and software configurations. Almost all network hardware responds to SNMP requests.

Network management tools now have access to data from almost all linked devices thanks to SNMP. In other words, any network management approach must include the widely adopted SNMP protocol.

As a result, IT managers utilize SNMP monitoring to find and control devices, learn about performance and availability, and ensure their network is operating properly.

Understanding that multiple versions of the SNMP protocol offer a wide range of features, particularly in terms of security, is crucial.

SNMPv1

SNMPv1, the original version, has few security measures. Managers can request information from agents using SNMPv1 without encrypting their communications.

Anyone with network access could use "sniffing" software to get network information. In addition, it implies that an unauthorized device might easily control the network by posing as a legal manager.

Additionally, because admins don't consistently update the default credentials used by SNMPv1, unauthorized parties can easily access important network data.

Unfortunately, due to some networks' lack of updating, SNMPv1 is still utilized on a large scale today.

SNMPv2

Although SNMPv2, which debuted in 1993, brought significant security improvements, it was replaced by SNMPv3, which is still the most recent and safe version of the protocol. 

SNMPv3

Data encryption is made feasible through SNMPv3. It enables administrators to define various authentication standards for managers and agents finely.

This stops unwanted authentication and, if desired, can be used to make data transmissions encrypted. The fact remains that while SNMPv1's security flaws gave it a bad reputation in some circles, SNMPv2, and especially SNMPv3, fixed those issues.

The more recent SNMP versions offer a modern, secure network monitoring method.

First, being an open standard protocol is one of SNMP's main benefits.

A variety of standard MIBs have been created, enabling monitoring tools to acquire metrics of interest from any device that supports the standard MIBs, regardless of model or manufacturer.

As an illustration, the MIB-II standard MIB enables network equipment to disclose data regarding the number of network interfaces they support and the volume of traffic flowing into and out of each interface (in addition to other statistics).

Any device that supports MIB-II can be polled by a monitoring system, which can automatically identify the device's interfaces and track bandwidth usage for each.

SNMP is mostly utilized for:

  • Automatic network equipment discovery - Vendor-specific MIBs categorize each network device.
  • Monitoring network topologies and connections are another capabilities of SNMP.
  • Polling network equipment to gather different metrics - Monitoring systems compare statistics reported by each network device over time to identify changes in network device status, workload information, and performance metrics (queue lengths, buffer overflows, packets dropped, etc.).
  • When irregularities are discovered, network devices also produce SNMP traps. For instance, a printer running low on paper may send a trap to its monitoring tool, alerting it that action is required.
  • Similar to how a network interface failure could result in a router sending a trap, monitoring tools can identify failure conditions administrators may need to be aware of by listening for and analyzing such traps.

SNMP frequently uses User Datagram Protocol (UDP) as its transport protocol. UDP 161 is used by SNMP Managers for polling SNMP Agents, and Agents use UDP 162 to communicate unauthorized SNMP traps to the SNMP Manager.

The Transmission Control Protocol (TCP) IPX, Ethernet, and other protocols can also support SNMP.

As a result, SNMP can be implemented through LAN using either the UDP or TCP protocol, albeit most SNMP packets are delivered over UDP.

All SNMP communications are sent between two entities: managers or servers and agents or clients. A centralized system called SNMP manager is used to communicate with network devices' SNMP agents.

Any network-connected equipment, including phones, printers, computers, and network switches, is an SNMP agent. Typically, the managing entity in a network has the SNMP manager installed. On the managed devices, the SNMP agents are normally installed.

This is how the procedure goes:

  • Using destination port 161, the SNMP manager at the top of your system delivers instructions to a network device or SNMP agent.
  • The agent will send an SNMP trap to the SNMP manager on port 162 if it needs to report something or react to a command.

The SNMP Manager can communicate with the SNMP Agent using one of two methodologies:

1.   Inquiry/Reply:

To the agent's UDP Port 161, the manager issues a command. With the provided OID, each request sends a single SNMP command (GET, GETNEXT, GETBULK, SET, etc.).

2.  Trap (unexpected occurrences):

The SNMP agent starts this conversation by sending events to the SNMP manager's port 162 as SNMP commands (TRAPS or INFORM). For the SNMP agent to be able to identify the SNMP manager, it must first be configured.

For sending and receiving requests, SNMP uses UDP port 161 of the SNMP agent, and for receiving traps from managed devices, SNMP uses UDP port 162 of the SNMP manager.

These port numbers must be the defaults for all SNMP-enabled devices. Since SNMP v1, these two ports have been the same in all SNMP versions.

Even if it's uncommon, some suppliers let you alter the default ports in the agent's configuration.

One of the most commonly used networking industry protocols, SNMP is supported on a wide range of hardware, including endpoints like printers, scanners, and IoT devices and standard network components like routers, switches, and wireless access points.

SNMP software can monitor Dynamic Host Configuration Protocol (DHCP) configuration services and the hardware.

In an environment with SNMP support, the following are the primary runtime components:

Devices and resources managed by SNMP

The devices and network components on which an agent runs are known as SNMP-managed devices and resources.

SNMP agent

This program runs on the hardware or service that SNMP is watching and gathers information on various metrics, such as CPU utilization, bandwidth use, or disk space. The agent locates and returns this data to SNMP management systems as requested by the SNMP manager.

SNMP manager

also known as an SNMP server—serves as a centralized management station that runs an SNMP management application across various operating system environments. It actively requests that agents submit periodic SNMP updates.

MIB: Management Information Base

This data structure, a text file with a mib file extension, lists all the data objects utilized by a certain device that may be accessed or managed via SNMP, including access control.

Numerous managed objects can be recognized within the MIB using Object Identifiers. A MIB identification called an Object Identifier (OID) is used to distinguish between devices inside the MIB.

OIDs are generated uniquely and are used to access MIB objects and environments. It actively requests that agents submit periodic SNMP updates.

The Simple Network Management Protocol employs one or more administrative SNMP managers to administer networks of connected computers and related devices.

The managers get information via SNMP from an agent, a software that runs continuously. The agents turn the data into variables and categorize them according to management information bases.

A combination of push and pull connections between network nodes and the network management system are used by SNMP tools to carry out many tasks.

Its basic capabilities include carrying out read and write instructions, including updating a configuration setting or resetting a password.

It can also determine how much CPU, memory, and network bandwidth are used.

If a predetermined threshold is exceeded, some SNMP managers could automatically send the administrator a text message or email or notice.

The message commands that the protocol supports are described in the following PDUs, or protocol data units:

  • Get request: A request to acquire the value of a variable or array of variables.
  • Set Request: A message sent to the agent by the SNMP manager to issue configurations or commands.
  • GetNext Request: Sent to the agent by the SNMP manager to retrieve the values of the subsequent record in the hierarchy of the MIB.
  • GetBulk Request: This command instructs the agent to issue several GetNext Requests to gather massive data tables.
  • SNMP Trap: Asynchronous trap messages from SNMP agents notify an SNMP manager that a major event, such as an error or failure, has happened. 
  • SNMP Response: Sent by the agent to the SNMP manager, provided in response to an SNMP Trap.
  • SNMP Inform: this command confirms receipt of a trap. 

A networking protocol called Simple Network Management Protocol (SNMP) is used in Internet Protocol networks to manage and keep track of network-connected devices.

Numerous local devices, including routers, switches, servers, firewalls, and wireless access points, all include the SNMP protocol and can be accessed by their IP address.

Network devices can relay management information using SNMP in single- and multi-vendor LAN or WAN contexts. In the OSI model framework, it is a protocol at the application layer.

Your network receives traffic from a variety of sources. The entire network and its components may communicate with one another thanks to Simple Network Management Protocol. As previously indicated, SNMP is set up on devices, and once the protocol is turned on, the devices will save their performance statistics.

There will be several Management Information Base (MIB) files on each network server. The monitoring data is retrieved by querying the device's MIB files. Each of SNMP's components contributes to managing resources, which is how it functions.

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Susith Nonis

I'm fascinated by the IT world and how the 1's and 0's work. While I venture into the world of Technology, I try to share what I know in the simplest way with you. Not a fan of coffee, a travel addict, and a self-accredited 'master chef'.