SNMP (Simple Network Management Protocol)

SNMP (Simple Network Management Protocol) is a protocol that lets a management system query and configure network devices and receive alerts from them. Each device exposes data, such as interface traffic counters, CPU load or temperature, as numbered objects described in a Management Information Base (MIB) and identified by an OID.

Why it matters

SNMP is the long-standing basis of network monitoring. A monitoring server polls devices (UDP port 161) every minute or so to graph bandwidth and detect failures, and devices can push unsolicited messages called traps (UDP port 162) when something changes, such as a link going down.

Versions matter for security. SNMPv1 and v2c authenticate with a plain-text "community string", while v3 adds real authentication and encryption.

Example

snmpget -v2c -c public 192.0.2.1 1.3.6.1.2.1.1.5.0

This asks the device at 192.0.2.1 for its system name (OID 1.3.6.1.2.1.1.5.0). Polling ifInOctets twice and dividing the difference by the interval gives inbound traffic rate.

Common mistakes

• Leaving the default community string public or private in place.
• Exposing SNMP to the internet, where it can leak topology or be abused in reflection attacks.
• Using v2c across untrusted networks instead of v3.

Related

• Router
• Network switch
• UDP
• Throughput

This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.