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Cellular backup (4G)

A 4G module is configured as an uplink like any other, almost always as a backup.

Where: Connectivity > Interfaces & network > Internet tab, Cellular card.

What the card shows

Field Meaning
Module The modem model. Unrecognised module means generic settings are used
Network Registration state, e.g. Registered on Orange (LTE) or Roaming on …
Signal Strength in % and dBm
IMEI The module's identity
Data address The address the mobile network assigned
Data carried Traffic over the link, for a metered SIM

Other states you may see: Searching for a network, Not registered on a network, The network refused this SIM, No SIM card detected, The SIM is locked and needs its PIN, The SIM is blocked and needs its PUK.

In use by the data link

While the link is up, the data connection holds the module, so the card shows the readings from the last time it could be read. This means the link is working.

A module that is present but not used says Detected but not used. Add it as an uplink to carry traffic.

Setting it up

  1. Under Role, choose a backup role (for example Backup 1). The device dials the module when the links above it are down.
  2. Open Cellular settings:
    • Automatic APN — read from the module each time it dials, so it follows the SIM if the card is changed. Leave it on unless your provider needs a specific APN.
    • APN — required when automatic APN is off.
    • Provider username and password — only a few providers need these.
    • SIM PIN — 4 to 8 digits; leave empty if the SIM has no PIN. Where you can, disable the PIN on the SIM instead. Remove stored PIN clears it.
  3. Click Save cellular settings, then apply and confirm the change.

When the module stops responding

The device tries to recover a silent module on its own. If that fails, a Reboot from the device overview power-cycles the module; it re-registers and dials by itself afterwards, with no site visit.

A gateway whose only uplink is cellular reboots itself after the module has been unreachable for 45 minutes, at most once every six hours. A gateway with a working wired uplink never reboots itself for this; reboot it yourself when you choose to.

When the backup does not take over

  • Network says searching or not registered — no network to dial: signal, antenna or SIM.
  • The uplink is down rather than standby — the device's probe cannot reach the internet through it; the SIM may have no data allowance.
  • The link is up but clients behind the gateway have no internet — usually outbound NAT, see Outbound NAT.