Understanding snmp

SNMP

Simple Network Mangement Protocol (SNMP) is a standard protocol used for monitoring, managing, and configuring devices on a network.

It enables network administrators to collect data, monitor performance, and identify issues on devices like routers, switches, servers, printers etc.

About SNMP:

Attribute	Description
OSI Layer	Application Layer (Layer 7)
Transport Protocol	UDP
Ports	161/UDP for agents communication, 162/USP for traps
Versions	SNMPv1, SNMPv2c, SNMPv3
Common Devices	Router switches, Server, printers, IoT Devices

Key components:

SNMP Manager:

• Central system that issues requests to gather data and control network devices.
• It is a centralized system used to monitor the network. It is also known as Network Management Station (NMS).

Responsibilities:

• Sends requests to SNMP agents (e.g., GET, SET, GETNEXT).
• Receives responses or TRAPs from SNMP agents.
• Maintains a centralized view of the network status.
• Logs, alerts and performs automated tasks.

Examples:

• SolarWinds
• Manage Engine
• Zabbix

SNMP Agent:

• SNMP agent is a software process running on networked devices.
• Software running on a managed devices that reponds to requests from SNMP manager.
• Collects and stores device specific information.

Responsibilities:

• Listens for SNMP requests on UDP port 161.
• Responds with requested info (e.g., Device uptime, CPU usage).
• Sends SNMP TRAPs or INFORMs to the manager to notify issues/events.
• Pull data from internal device metrics and make it accessible.

Examples:

• snmpd on Linux
• Bulit-in agents in Cisco/Juniper devices.

MIB:

• Management Information Base (MIB) is a virtual database (a hierarchical structure) that defines what information an SNMP agent can provide.
• Defines the data objects that can be managed on a device.

Responsibilities:

• Standardize all the device info (uptime, interfaces, errors, etc.)
• Defined Object Identifiers (OIDs): Unique addresses to data points.
• Both manager and agent refer to the MIB to understand each other.

Examples:

• sysDescr.0: System description
• OID: .1.3.6.1.2.1.1.1.0

Installation of SNMP agent on Linux:

Installation:

1. First update your system.

    sudo apt update
   

2. Then install SNMP using apt:

    sudo apt install snmp snmpd
   

3. Check if it is installed or not:

    sudo systemctl status snmpd
   

   

Configuration:

Edit the config file:

sudo nano /etc/snmp/snmpd.conf

Common changes:

rocommunity public
agentAddress udp:161
sysLocation "Author's machine"
sysContact [email protected]

Reload the SNMP service:

sudo systemctl restart snmpd

Test SNMP:

snmpwalk -v2c -c public localhost

Output:

Displaying System Description:

snmpwalk -v2c -c public localhost 1.3.6.1.2.1.1.1.0

Common SNMP OIDs and Their Uses:

OID	Name	MIB	Description / Use
.1.3.6.1.2.1.1.1.0	sysDescr.0	SNMPv2-MIB	Describes system: OS, version, hardware, etc.
.1.3.6.1.2.1.1.3.0	sysUpTime.0	SNMPv2-MIB	Time since the device last rebooted
.1.3.6.1.2.1.1.5.0	sysName.0	SNMPv2-MIB	Hostname of the device
.1.3.6.1.2.1.1.4.0	sysContact.0	SNMPv2-MIB	Contact person for this device
.1.3.6.1.2.1.1.6.0	sysLocation.0	SNMPv2-MIB	Physical location of the device
.1.3.6.1.2.1.2.2.1.2.X	ifDescr.X	IF-MIB	Description of interface X
.1.3.6.1.2.1.2.2.1.8.X	ifOperStatus.X	IF-MIB	Interface status: up/down/testing
.1.3.6.1.2.1.2.2.1.10.X	ifInOctets.X	IF-MIB	Bytes received on interface X
.1.3.6.1.2.1.2.2.1.16.X	ifOutOctets.X	IF-MIB	Bytes sent out on interface X
.1.3.6.1.2.1.25.1.1.0	hrSystemUptime	HOST-RESOURCES-MIB	System uptime in hundredths of a second
.1.3.6.1.2.1.25.2.3.1.6.X	hrStorageUsed.X	HOST-RESOURCES-MIB	Amount of used storage in block units
.1.3.6.1.2.1.25.3.3.1.2.X	hrProcessorLoad.X	HOST-RESOURCES-MIB	CPU load of processor X
.1.3.6.1.4.1.2021.4.5.0	memTotalReal	UCD-SNMP-MIB	Total physical RAM
.1.3.6.1.4.1.2021.4.6.0	memAvailReal	UCD-SNMP-MIB	Available physical RAM
.1.3.6.1.4.1.2021.11.9.0	ssCpuIdle	UCD-SNMP-MIB	% of CPU time spent idle
.1.3.6.1.4.1.2021.10.1.3.1	laLoad.1	UCD-SNMP-MIB	1-minute load average