LTE Signal Monitoring and Failover

LTE Signal Monitoring and Failover

This guide covers the operational aspects of LTE management in RouterOS: interpreting signal quality metrics, configuring APN profiles, setting up LTE as a backup WAN, and using SMS for remote modem control.

Signal Monitoring

RouterOS provides real-time access to cellular radio metrics through the LTE interface monitor and info commands.

Monitoring Commands

View live signal metrics:

/interface lte monitor [find]

Continuous monitoring at a fixed interval:

/interface lte monitor [find] interval=5s

One-shot modem and connection details (IMEI, firmware, registration state):

/interface lte info [find] once

Signal Metrics Reference

Metric	Full Name	Good	Acceptable	Poor
rssi	Received Signal Strength Indicator	> −85 dBm	−85 to −100 dBm	< −100 dBm
rsrp	Reference Signal Received Power	> −80 dBm	−80 to −95 dBm	< −95 dBm
rsrq	Reference Signal Received Quality	> −10 dB	−10 to −15 dB	< −15 dB
sinr	Signal to Interference + Noise Ratio	> 20 dB	10 to 20 dB	< 10 dB
cqi	Channel Quality Indicator	10–15	6–9	< 6

RSRP is the most reliable indicator of coverage — it measures received power on the LTE reference signal, independent of interference. RSRQ and SINR reflect signal quality relative to noise and interference. A good RSRP with poor SINR indicates interference rather than distance from the tower.

Example Monitor Output

         pin-status: ok
  registration-state: registered
            operator: 310410
                 lac: c000
                  ci: 00001037
                  ip: 10.100.13.145
             gateway: 10.100.13.146
         pdp-context: active
                rssi: -75
                rsrp: -92
                rsrq: -10
                sinr: 12

Script-Based Signal Alerting

Log a warning when RSRP drops below a threshold:

/system script add name=lte-signal-check source={
    :local rsrp [/interface lte get [find] rsrp]
    :if ($rsrp < -95) do={
        /log warning ("Weak LTE signal - RSRP: " . $rsrp . " dBm")
    }
}

/system scheduler add name=lte-signal-poll interval=5m \
    on-event=lte-signal-check

APN Configuration

APN (Access Point Name) profiles define how RouterOS connects to the carrier’s data network. Configure them in /interface lte apn, then assign to the LTE interface.

Sub-menu: /interface lte apn

Creating an APN Profile

Basic profile with no authentication (most consumer carriers):

/interface lte apn add name=internet apn=internet

Profile with PAP authentication:

/interface lte apn add name=carrier-auth \
    apn=internet \
    authentication=pap \
    user=user@carrier.net \
    password=pass

Profile using the SIM/network-provided APN:

/interface lte apn add name=network-apn use-network-apn=yes

Assigning the Profile

/interface lte set [find] apn-profiles=internet

APN Properties

Property	Values	Description
name	string	Profile name
apn	string	Access Point Name string from carrier
authentication	none, pap, chap	Auth method; default none
user	string	Username for PAP/CHAP
password	string	Password for PAP/CHAP
ip-type	ipv4, ipv6, ipv4-ipv6, auto	Requested PDP type
use-network-apn	yes, no	Use SIM-provided APN instead of specifying one
add-default-route	yes, no	Automatically add default route via LTE
default-route-distance	integer	Admin distance for the auto-added default route
passthrough-interface	interface name	Interface that receives the modem’s public IP via DHCP

Note

ip-type=auto is the safest choice when the carrier’s PDP type support is unknown. Requesting ipv6 on a carrier that does not support it will prevent attachment.

LTE Passthrough

Passthrough passes the modem’s public IP address directly to a downstream device via DHCP. Only one DHCP client receives the passthrough lease.

/interface lte apn add name=passthrough-apn \
    apn=internet \
    passthrough-interface=ether1

/interface lte set [find] apn-profiles=passthrough-apn

/ip dhcp-client add interface=ether1 disabled=no

Caution

Passthrough is not supported on all modem chipsets. Only IPv4 is supported in passthrough mode.

LTE as Backup WAN

The simplest and most reliable way to configure LTE failover is using administrative distance on the default route. RouterOS selects the lowest-distance valid route; when the primary WAN fails, the higher-distance LTE route becomes active.

Static Distance-Based Failover

# Primary WAN default route (low distance — preferred)
/ip route add dst-address=0.0.0.0/0 gateway=192.0.2.1 distance=1 comment=primary-wan

# LTE backup route (higher distance — standby)
/ip route add dst-address=0.0.0.0/0 gateway=lte1 distance=10 comment=lte-backup

When the primary gateway becomes unreachable (interface goes down, gateway unreachable), RouterOS automatically promotes the LTE route.

Note

The LTE APN profile must have add-default-route=yes disabled if you are adding the LTE route manually, to avoid duplicate default routes.

Netwatch Health-Check Failover

Static distance failover only detects physical link failure. Use Netwatch to detect internet reachability loss and adjust route distances accordingly:

# Lower primary WAN route priority when internet probe fails
/tool netwatch add host=1.1.1.1 interval=10s timeout=3s \
    down-script="/ip route set [find comment=primary-wan] distance=20" \
    up-script="/ip route set [find comment=primary-wan] distance=1"

Probe through the primary interface specifically to avoid false positives when LTE is active:

/tool netwatch add host=1.1.1.1 interval=10s timeout=3s \
    src-address=<primary-wan-ip> \
    down-script="/ip route set [find comment=primary-wan] distance=20" \
    up-script="/ip route set [find comment=primary-wan] distance=1"

Recursive Route Failover

Recursive routing ensures routes are only valid when their nexthop is reachable. This gives automatic failover without scripting:

# Host routes for probing — one per WAN
/ip route add dst-address=1.1.1.1/32 gateway=<primary-gw>
/ip route add dst-address=8.8.8.8/32 gateway=lte1

# Recursive default routes through probes
/ip route add dst-address=0.0.0.0/0 gateway=1.1.1.1 distance=1 check-gateway=ping
/ip route add dst-address=0.0.0.0/0 gateway=8.8.8.8 distance=10 check-gateway=ping

Scripted Failover with Notifications

For more control — including hysteresis, logging, and SMS alerts on failover events:

/system script add name=wan-failover-down source={
    /ip route set [find comment=primary-wan] distance=20
    /log warning "Primary WAN down: activating LTE backup"
    /tool sms send port=lte1 phone-number=+1234567890 \
        message="Router: primary WAN down, LTE backup active"
}

/system script add name=wan-failover-up source={
    /ip route set [find comment=primary-wan] distance=1
    /log info "Primary WAN restored"
    /tool sms send port=lte1 phone-number=+1234567890 \
        message="Router: primary WAN restored"
}

/tool netwatch add host=1.1.1.1 interval=10s timeout=3s \
    down-script=wan-failover-down \
    up-script=wan-failover-up

SMS Commands for Modem Control

RouterOS supports sending and receiving SMS messages through /tool sms. SMS can be used to check router status, trigger scripts, and control the router remotely.

Enabling SMS

/tool sms set enabled=yes port=lte1

Sending SMS

/tool sms send port=lte1 phone-number=+1234567890 \
    message="LTE backup active — primary WAN down"

Reading the SMS Inbox

/tool sms inbox print

Delete read messages:

/tool sms inbox remove [find]

Remote Control via SMS

RouterOS can execute commands or scripts triggered by incoming SMS messages. Enable receive mode and set a secret passphrase:

/tool sms set enabled=yes receive-enabled=yes port=lte1 secret=mysecret

Send an SMS from an authorized number in this format to execute a command:

mysecret /ip address print

Or to run a saved script:

:cmd mysecret script-name

Restrict to specific numbers for security:

/tool sms set allowed-number=+1234567890

Caution

Always set a strong secret and restrict allowed-number when enabling SMS command execution. Without these controls, anyone who can send an SMS to the SIM can execute commands on the router.

Common SMS Control Use Cases

Use Case	SMS Message Format
Check CPU/memory	mysecret :put [/system resource get cpu-load]
Reboot router	mysecret /system reboot
Check LTE signal	mysecret :put [/interface lte get lte1 rsrp]
Enable/disable interface	mysecret /interface enable ether1

AT Commands via LTE Interface

For advanced modem interaction, send AT commands directly:

/interface lte at-chat lte1 input="AT+CSQ"

Common AT commands for diagnostics:

AT Command	Purpose
AT+CSQ	Signal quality (RSSI, BER)
AT+CREG?	Network registration status
AT+COPS?	Current operator
AT+CPSI?	Detailed system info (band, earfcn, etc.)
AT+CIMI	IMSI of SIM

Note

AT command availability and behavior varies by modem model and firmware version.

Troubleshooting

Verify LTE Route Is Active

/ip route print where comment~"lte"

Check Primary vs Backup Route Selection

/ip route print where dst-address=0.0.0.0/0

The route with the lowest distance and a valid gateway (R flag) is the active one.

Test Connectivity Through LTE Specifically

/ping 8.8.8.8 interface=lte1 count=5

Reset LTE Interface

/interface lte reset [find]

Check System Logs for LTE Events

/log print where message~"lte"

Related Topics

• LTE/5G - Full LTE interface reference including band locking, eSIM, and carrier aggregation
• SMS - Detailed SMS configuration and scripting
• Dual SIM Application - Automatic SIM switching and multi-carrier failover
• Mobile Networking Overview - General mobile networking guide
• Firewall and Quality of Service - Traffic shaping for LTE