What is SNMP and how do I use it to monitor switches?

SNMP (Simple Network Management Protocol) is the industry standard for monitoring and managing network devices.

SNMP Versions

• SNMPv1: Legacy, plaintext community strings, avoid
• SNMPv2c: Most common, adds bulk operations, still plaintext
• SNMPv3: Adds authentication and encryption — recommended

Key Components

• Agent: Runs on the switch, responds to queries
• Manager (NMS): Central monitoring system (e.g., Zabbix, PRTG, SolarWinds)
• MIB (Management Information Base): Hierarchical database of variables
• OID (Object Identifier): Numeric address for MIB variables
• Traps: Unsolicited notifications from device

Common Monitored Items

• Port up/down status (ifOperStatus)
• Bandwidth utilization (ifInOctets/ifOutOctets)
• CPU and memory usage
• Temperature (in industrial switches)
• PoE power draw per port
• Optical DDM values (SFP temp, Tx/Rx power)

Setup Best Practices

1. Use SNMPv3 with authPriv wherever possible
2. Restrict SNMP access to management VLAN
3. Use ACLs to limit source IPs
4. Configure SNMP traps for critical events (port down, temp high)
5. Poll intervals: 5min for stats, 30s for critical

Popular NMS Tools

• PRTG Network Monitor
• Zabbix (open-source)
• LibreNMS (open-source)
• SolarWinds NPM
• Nagios/Icinga