Dual SIM Application

Dual SIM Application

The Dual SIM Application enables automatic switching between SIM slots on MikroTik devices with LTE/5G modems. This functionality is essential for mobile vehicle applications where routers travel across borders and need to use different SIM cards for home and roaming networks.

Overview

Dual SIM switching enables intelligent SIM card selection based on network conditions. Two primary use cases exist:

• Roaming-based switching: Automatically use a local SIM card when roaming is detected, switching back to the home SIM when roaming ends
• Failover-based switching: Switch to the alternative SIM when the current connection is lost

Both scripts require scheduling to run periodically, checking network conditions and performing SIM switches when necessary.

Sub-menu

The dual SIM functionality uses several RouterOS sub-menus:

• /interface lte - LTE interface configuration
• /system routerboard sim - SIM slot management (RouterOS v6.45 and earlier)
• /system routerboard modem - Modem SIM slot management (RouterOS v6.45.1+)
• /interface lte settings - SIM slot configuration (RouterOS v7)
• /system script - Script execution
• /system scheduler - Scheduled task execution

Supported Devices

Dual SIM functionality is available on MikroTik devices with LTE modems and dual SIM slots, including:

• LtAP mini series
• LtAP series
• SXT LTE series
• wAP LTE series
• Other devices with dual SIM capability

Note

SIM slot naming varies by device. Some devices use “up” and “down” slots, while others use “a” and “b” nomenclature.

Initial Configuration

LTE Interface Setup

Before configuring dual SIM, ensure LTE network parameters are correctly configured for each SIM card. Use the default APN profile or create separate profiles for each SIM:

/interface lte apn add apn=internet.example.com name=sim1-home
/interface lte apn add apn=internet.roaming.com name=sim2-roaming

For detailed LTE setup instructions, see the LTE/5G Quick Setup Guide.

Enable Data Roaming

Enable data roaming to allow connection to foreign network providers:

/interface lte set [find name=lte1] allow-roaming=yes

This setting is essential for tracking roaming status and enabling automatic SIM switching.

Configure SIM Slots

Configure which SIM slots correspond to home and roaming networks. The command syntax varies by RouterOS version:

RouterOS v6.45 and earlier:

/system routerboard sim set sim-slot=down

RouterOS v6.45.1+:

/system routerboard modem set sim-slot=down

RouterOS v7:

/interface lte settings set sim-slot=down

Caution

When changing SIM slots, the LTE modem restarts. This process takes approximately 30 seconds depending on the modem and device. Always test your configuration after making changes.

Roaming Script

The roaming script automatically switches SIM cards based on roaming detection. Use the home SIM when on the home network and switch to the roaming SIM when traveling abroad.

Creating the Roaming Script

Create a script named “roamingScript” in /system/script:

/system script add name=roamingScript source={
# Setup and read current values
:global simSlot [/system routerboard sim get sim-slot]
:global timeoutLTE 60
:global timeoutConnect 60

# Wait for LTE to initialize for maximum "timeoutLTE" seconds
:local i 0
:local isLTEinit false
:while ($i<$timeoutLTE) do={
    :foreach n in=[/interface lte find] do={:set $isLTEinit true}
    :if ($isLTEinit=true) do={
        :set $i $timeoutLTE
    }
    :set $i ($i+1)
    :delay 1s
}

# Check if LTE is initialized, or try power-reset the modem
:if ($isLTEinit=true) do={
    # Wait for LTE interface to connect to mobile network
    :local isConnected false
    :set $i 0
    :while ($i<$timeoutConnect) do={
        :if ([/interface lte get [find name="lte1"] running]=true) do={
            :set $isConnected true
            :set $i $timeoutConnect
        }
        :set $i ($i+1)
        :delay 1s
    }
    # Check if LTE is connected
    if ($isConnected=true) do={
        :local Info [/interface lte monitor lte1 once as-value]
        :local isRoaming ($Info->"roaming")
        # Check which SIM slot is used
        :if ($simSlot="down") do={
            # If "down" (home) slot, check roaming status
            :if ($isRoaming=true) do={
                :log info message="Roaming detected, switching to SIM UP (Roaming)"
                /system routerboard sim set sim-slot=up
            }
        } else={
            # Else "up" (roaming) slot, check roaming status
            :if (!$isRoaming=true) do={
                :log info message="Not roaming, switching to SIM DOWN (Home)"
                /interface lte settings set sim-slot=down
            }
        }
    } else={
        :log info message="LTE interface did not connect to network, wait for next scheduler"
    }
} else={
    :log info message="LTE modem did not appear, trying power-reset"
    /system routerboard usb power-reset duration=5s
}
}

Script Behavior

The roaming script performs the following actions:

1. Initialization Check: Waits up to 60 seconds for the LTE interface to appear
2. Connection Verification: Waits up to 60 seconds for the interface to enter “running” state
3. Roaming Detection: Monitors the roaming status from LTE interface information
4. SIM Switching Logic:
   • If on “down” (home) slot and roaming detected → switch to “up” (roaming) slot
   • If on “up” (roaming) slot and not roaming → switch to “down” (home) slot
5. Failure Recovery: If LTE modem fails to initialize, performs a USB power reset

Configuration Variables

Variable	Description	Default
simSlot	Current SIM slot selection	Retrieved from system
timeoutLTE	Maximum wait time for LTE initialization	60 seconds
timeoutConnect	Maximum wait time for network connection	60 seconds

Failover Script

The failover script switches SIM cards when the current connection is lost, providing resilience against network outages.

Creating the Failover Script

Create a script named “failoverScript” in /system/script:

/system script add name=failoverScript source={
# Setup and read current values
:global simSlot [/system routerboard modem get sim-slot]
:global timeoutLTE 60
:global timeoutConnect 60

# Wait for LTE to initialize for maximum "timeoutLTE" seconds
:local i 0
:local isLTEinit false
:while ($i<$timeoutLTE) do={
    :foreach n in=[/interface lte find] do={:set $isLTEinit true}
    :if ($isLTEinit=true) do={
        :set $i $timeoutLTE
    }
    :set $i ($i+1)
    :delay 1s
}

# Check if LTE is initialized, or try power-reset the modem
:if ($isLTEinit=true) do={
    # Wait for LTE interface to connect to mobile network
    :local isConnected false
    :set $i 0
    :while ($i<$timeoutConnect) do={
        :if ([/interface lte get [find name="lte1"] running]=true) do={
            :set $isConnected true
            :set $i $timeoutConnect
        }
        :set $i ($i+1)
        :delay 1s
    }
    # Check if LTE is connected
    if ($isConnected=false) do={
    # Check which SIM slot is used
        :if ($simSlot="down") do={
            # If "down" slot, switch to up
        :log info message="LTE down, switching slot to UP"
            /interface lte settings set sim-slot=up
    }
        :if ($simSlot="up") do={
            # If "up" slot, switch to down
        :log info message="LTE down, switching slot to DOWN"
            /interface lte settings set sim-slot=down
            }
        } else={
            # Else "running"
            :if ($isConnected=true) do={
                :log info message="LTE UP"
            } else={
        :log info message="LTE interface did not connect to network, wait for next scheduler"
        }
    }
    } else={
    :log info message="LTE modem did not appear, trying power-reset"
    /system routerboard usb power-reset duration=5s
}
}

Script Behavior

The failover script operates as follows:

1. Initialization Check: Waits up to 60 seconds for the LTE interface to appear
2. Connection Detection: Checks if the LTE interface is in “running” state
3. SIM Switching Logic:
   • If current slot is “down” and connection is down → switch to “up”
   • If current slot is “up” and connection is down → switch to “down”
4. Status Logging: Logs connection status changes

Caution

The failover script only switches when the current SIM cannot connect. To switch back to the primary SIM, configure a time-based scheduler or use the roaming script in conjunction.

Scheduler Configuration

Create schedulers to run the scripts periodically. A 3-minute interval is recommended to prevent overlapping executions.

Roaming Scheduler

/system scheduler add interval=3m on-event=roamingScript name=Roaming

Failover Scheduler

/system scheduler add interval=3m on-event=failoverScript name=Failover

Scheduler Properties

Property	Description	Default
interval	Time between script executions	3m recommended
on-event	Script to execute	roamingScript or failoverScript
name	Scheduler identifier	User-defined
start-time	First execution time	startup
disabled	Enable/disable scheduler	no

Scheduler Interval Considerations

Use Case	Recommended Interval
High mobility (vehicles)	1m - 2m
Standard roaming scenarios	3m - 5m
Low mobility / infrequent travel	10m - 15m

Caution

Avoid intervals shorter than 1 minute, as SIM switching requires approximately 30 seconds to complete. Overlapping executions may cause unexpected behavior.

Viewing SIM Status

Check Current SIM Slot

RouterOS v6.45 and earlier:

/system routerboard sim print

RouterOS v6.45.1+:

/system routerboard modem print

RouterOS v7:

/interface lte settings print

Monitor LTE Interface Status

/interface lte monitor lte1 once

Output includes roaming status, signal strength, and connection state.

View Interface Details

/interface lte print detail

Troubleshooting

SIM Slot Change Not Taking Effect

1. Verify RouterOS version compatibility with the command syntax
2. Check that the modem supports dual SIM operation
3. Review system logs for error messages
4. Perform a modem power cycle manually:

/system routerboard usb power-reset duration=10s

LTE Interface Not Initializing

1. Verify LTE modem is properly installed
2. Check SIM cards are correctly inserted
3. Confirm antenna connections are secure
4. Review LTE interface configuration:

/interface lte print

Excessive Roaming Data Usage

Roaming data may be consumed on the home SIM if:

• The home SIM has roaming enabled
• The script switches back and forth frequently
• Network conditions cause rapid status changes

Consider these optimizations:

• Increase scheduler interval to reduce checks
• Implement hysteresis in the roaming detection
• Use time-based restrictions for roaming SIM usage

Scripts Not Executing

1. Verify scripts exist in /system/script
2. Check scheduler is not disabled
3. Review execution logs:

/log print where message~"LTE"

Modem Does Not Restart After SIM Change

1. Verify the modem model supports hot-swap
2. Check for sufficient power supply
3. Review USB power-reset configuration
4. Consider a hardware reboot if persistent

Best Practices

Testing Before Deployment

1. Test SIM switching manually before automating
2. Verify roaming detection works correctly
3. Measure SIM switch timing on your specific device
4. Test failover scenarios in a controlled environment

Production Deployment

1. Use descriptive names for scripts and schedulers
2. Document which slot corresponds to which SIM
3. Implement monitoring for SIM switch events
4. Set appropriate timeout values based on testing
5. Regular review of data usage on each SIM

Data Usage Monitoring

Monitor data consumption on both SIM cards:

/interface lte monitor lte1 once

Track usage through your mobile operator’s portal or API.

Logging Configuration

Enable comprehensive logging for troubleshooting:

/system logging add topics=interface,lte,debug

Review logs with:

/log print where message~"LTE"

Related Commands

• /interface lte - LTE interface management
• /interface lte monitor - LTE connection monitoring
• /interface lte settings - LTE settings (v7)
• /system routerboard sim - SIM management (RouterOS v6.45 and earlier)
• /system routerboard modem - Modem management (RouterOS v6.45.1+)
• /system routerboard usb - USB power management
• /system script - Script management
• /system scheduler - Task scheduling

Related Resources

• Official MikroTik Dual SIM Documentation
• LTE/5G Overview
• Mobile Networking Overview
• RouterOS Scripting Manual
• Scheduler Documentation