Networking
SNMP
Also known as: Simple Network Management Protocol
SNMP (Simple Network Management Protocol) is the standard protocol for monitoring and managing network devices — querying switches, routers, UPSes, and servers for performance data and receiving alerts when something goes wrong.
SNMP lets management software poll network devices for status information and receive unsolicited alerts (traps) when something notable happens. A switch reports interface error counts, traffic utilization, and CPU load. A UPS reports battery level and input voltage. A server reports disk health and fan status.
SNMP uses a hierarchical data model called a MIB (Management Information Base) — a structured list of every variable the device exposes. Each variable has an OID (Object Identifier). A monitoring platform knows which OIDs to query for which data.
SNMP versions
SNMPv1 and v2c — community string authentication, effectively a cleartext password. Still widely used; adequate on a managed network but not internet-exposed. v2c adds bulk queries.
SNMPv3 — adds encryption and proper authentication. Should be used wherever SNMP traffic crosses less-trusted network segments.
SNMP operations
GET — management station requests a specific OID value from a device.
TRAP / INFORM — device sends an alert to the management station when a threshold is crossed or an event occurs. (INFORMs require acknowledgment; traps don't.)
SET — management station writes a value to the device — used for configuration changes via SNMP.
Most network monitoring tools (PRTG, LibreNMS, Zabbix, Domotz) use SNMP extensively. Configuring SNMP community strings or v3 credentials on your switches and UPSes is a prerequisite for useful network monitoring.