How to monitor an SNMP device in Checkmk

Monitoring an SNMP device in Checkmk adds switches, routers, printers, UPS units, and other appliances without installing a Checkmk agent on the device. The device exposes read-only SNMP data, and Checkmk uses that data to discover interfaces, sensors, uptime, and device information.

Checkmk stores the device as a host object. For an SNMP-only device, Checkmk agent / API integrations is set to No API integrations, no Checkmk agent, the SNMP option is enabled, and the SNMP credentials field stores the community string or SNMPv3 security parameters.

Enable SNMP on the device before saving the host, and allow requests from the Checkmk server or relay. The connection test should show the device's sysDescr, sysName, and related system fields; service discovery should then find the expected network interfaces, SNMP Info, and Uptime services.

1. Enable read-only SNMP access on the device for the Checkmk server or Checkmk Relay address.

   Use the device's own management interface to permit the monitoring server, choose SNMPv2c or SNMPv3, and record the community string or security settings before opening Checkmk.

2. Sign in to the Checkmk site with permission to edit hosts and activate changes.
3. Open Setup → Hosts → Hosts.
4. Open the folder that should contain the network device.
5. Create a host for the device or open the existing host properties.

   Use the device name that operators should see in monitoring, and enter its DNS name or management IP address when the name is not resolvable.
   Related: How to add a host in Checkmk

6. Set Checkmk agent / API integrations to No API integrations, no Checkmk agent in the Monitoring agents box.
7. Enable SNMP in the same Monitoring agents box and select SNMPv2 or v3.

   Use SNMP v1 only for old devices that cannot answer SNMPv2c queries because it lacks bulk access and is slower on interface-heavy devices.

8. Enter the device credentials under SNMP credentials.

   SNMPv2c community strings are transmitted without encryption. Use a management network or SNMPv3 authentication and privacy settings when the traffic crosses untrusted network segments.

9. Save the host with Save & go to connection test.
10. Confirm that the connection test returns sysDescr, sysContact, sysName, and sysLocation fields.

    sysDescr identifies the device model for automatic service discovery, while sysName should normally match the Checkmk host name so search and reports stay clear.

11. Run service discovery for the host.

    Use Full service scan for a new SNMP device or after changing credentials, device firmware, or reachable OID ranges because it forces Checkmk to scan for matching SNMP check plug-ins.
    Related: How to run Checkmk service discovery

12. Review the discovered services before accepting them.

    SNMP Info and Uptime should appear on most SNMP devices. Switches and routers should also show expected interface services, and appliances may show temperature, fan, power, RAID, or vendor-specific sensors.

13. Move only the intended services to monitoring or click Accept all when every discovered service should be monitored.

    Do not accept vanished or unwanted interface services without checking the device state; discovery changes the service configuration that will be activated later.

14. Activate the pending changes.

    Activation publishes the host, SNMP credentials, discovered services, and any changed discovery settings into the running monitoring environment.
    Related: How to activate Checkmk pending changes

15. Open the device from Monitor and check the service list.
16. Confirm that the expected SNMP Info, Uptime, and device-specific services appear without unhandled discovery warnings.
17. Create an SNMP walk from the Checkmk site shell when command-line evidence is required.

    OMD[mysite]:~$ cmk -v --snmpwalk core-switch-01
    core-switch-01:
    Walk on ".1.3.6.1.2.1"...2198 variables.
    Walk on ".1.3.6.1.4.1"...841 variables.
    Wrote fetched data to /omd/sites/mysite/var/check_mk/snmpwalks/core-switch-01.

    Replace core-switch-01 with the Checkmk host name. The command must run as the site user on the site that monitors the device.