Verify the cellular modem control port before assigning OPNsense WAN

Bottom line: Confirm which modem control port responds and whether the SIM is ready before configuring the provider connection. Keep the guide’s example ports and subscription settings separate from the site’s approved values.

Source fact: what the authority says

The OPNsense cellular-modem guide warns that devices behave differently and may require device-specific AT commands. Its control-port procedure sends AT and looks for an OK response. The SIM check uses AT+CPIN?, with +CPIN: READY in the example response; the guide notes that an undetected SIM or a PIN can prevent readiness. The PPP settings shown in the guide are explicitly an example for a Dutch KPN subscription.

What the source does not establish

This article covers port identification and readiness checks, not a modem compatibility guarantee or a universal carrier profile. It does not recommend removing SIM protection, resetting equipment or adopting the example subscription credentials.

Applicability questions

• Which exact modem model, firmware and provider subscription are being reviewed?
• Which detected device is its responding control port?
• What SIM state is observed without changing its security settings?
• Who supplied the approved APN and connection values for this subscription?

DSE recommendation: controlled next steps

The following steps are DSE recommendations based on the cited source.

DSE recommends a modem connection sheet with hardware identity, detected ports, tested control port and SIM state. Keep this separate from the WAN interface assignment. Have the installer compare the actual card and cabling with the hardware information rather than inferring a port number from the screenshot.

Use the documented status-query approach only within the approved maintenance procedure. Keep the initial exchange limited to identifying the responding port and reading the SIM state. If readiness is absent, record the exact response and involve the authorized SIM or hardware owner before issuing any command that changes protection or device configuration.

Obtain the APN and other subscription parameters from the provider or the organization’s approved connection record. Mark the guide’s example values as examples in the worksheet. Ask the network owner to review the intended WAN and gateway change before assigning the modem connection to an existing live WAN role.

Prepare a separate service check for the proposed cellular connection and preserve the current primary connection settings. Define whether the trial may affect routing, billing or limited mobile data. Keep an independent management route and agree when to abandon the pilot instead of repeatedly resetting a device to chase an unexplained response.

Verification and evidence

Proposed verification: record the actual responding control port, the AT response and the SIM-status response without retaining a SIM PIN. Compare the resulting connection settings with the approved provider profile. Check the effective WAN assignment only after the hardware and subscription entries have been reconciled.

Exercise a small permitted application request through the intended cellular path and record the observed address, route and connection state. Treat control-port response, SIM readiness and upstream service as three separate observations. Escalate a mismatch at the corresponding stage rather than accepting one successful local modem query as internet availability.

Official references

• OPNsense — Configuring Cellular Modems — official product documentation; confirm the installed release and configuration.

Source review completed October 29, 2026. Recheck the official documentation and deployment-specific applicability before a production change.