SNMP: the language of network devices
SNMP (Simple Network Management Protocol) is how NMS tools like Grafana, Zabbix, and PRTG ask network devices for metrics. Every router and switch runs an SNMP agent that exposes a MIB (Management Information Base) — a tree of variables identified by OIDs (Object Identifiers).
Common OIDs: interface counters, CPU usage, memory, error rates, interface status.