Active SIM card switching available on FortiGates with cellular modem and dual SIM card support

This information is also available in the FortiOS 7.4 Administration Guide: Active SIM card switching

FortiGates with a cellular modem and dual SIM card can switch in real time from the active SIM card to the passive SIM card when any of the following issues arise with the active SIM card:

• Ping link monitor fails. The SIM switch time depends on the link monitor parameters set.
• An active SIM card cannot be detected. The SIM switch time is about 20 seconds after the SIM card is no longer detected.
• A modem disconnection is detected, and a specified interval has elapsed. The SIM switch time occurs after the specified interval.

SIM card switching events are captured in the FortiGate event log.

In most cases, SIM cards come with the wireless carrier's APN, which is automatically retrieved at the first connection of the LTE modem. For these cases, you can use SIM cards for different wireless carriers in SIM slot 1 and slot 2. When one or both SIM cards require their APN settings to be configured on the FortiGate, then both SIM cards should be for the same wireless carrier because config system lte-modem currently only supports a single set apn < apn > setting.

The following command and options can be used to configure this feature:

config system lte-modem
    config sim-switch
        set by-sim-state {enable | disable}
        set by-connection-state {enable | disable}
        set by-link-monitor {enable | disable}
        set link-monitor <link-monitor-name>
        set sim-switch-log-alert-interval <interval>
        set sim-switch-log-alert-threshold <threshold>
        set modem-disconnection-time <integer>
    end
end

by-sim-state {enable | disable}	Enable switching based on active SIM card state: enable: switch to the passive SIM card whenever FortiGate cannot detect the active SIM card, such as when the active SIM card is ejected. disable: do not switch SIM cards based on state.
by-connection-state {enable | disable}	Enable switching based on the connection state of the active SIM card: enable: switch to the passive SIM card whenever FortiGate detects a modem signal loss after the modem-disconnection-time expires. disable: do not switch SIM cards based on the connection state.
by-link-monitor {enable | disable}	Enable switching when a configured link monitor fails: enable: switch to the passive SIM card when a link monitor configured with link-monitor-name fails. disable: do not switch SIM cards based on the failure of a configured link monitor.
link-monitor <link-monitor-name>	Specify the name of the link monitor to use with by-link-monitor.
sim-switch-log-alert-interval <interval>	Identify what number of constant SIM card switch events will trigger an event log after the threshold in sim-switch-log-alert-threshold is met.
sim-switch-log-alert-threshold	Specify how many minutes to wait before creating an event log when the number of SIM card switches defined in sim-switch-log-alert-interval is met.
modem-disconnection-time <integer>	Specify how many seconds to wait before switching over to the passive SIM card when by-connection-state is enabled and a modem signal loss is detected.

Example 1

In this example, automatic SIM card switching is disabled. When disabled, the SIM card only works in the default slot1, but you can manually switch the SIM card to slot2. Event logs include details about the SIM card switch.

To manually switch a SIM card:

1. Disable automatic SIM card switching:

   config system lte-modem
       config sim-switch
           set by-sim-state disable
           set by-connection-state disable
           set by-link-monitor disable
           set sim-slot 1
       end
   end

2. Manually switch the SIM card from slot1 to slot2, and run the following command:

   # execute lte-modem sim-switch

   The SIM card switch may take a few seconds. You can run diagnose system lte-modem sim-info to check the results.

   The following log is generated after unplugging an active SIM card:

   7: date=2023-05-02 time=10:41:05 eventtime=1683049264795418820 tz="-0700" logid="0100046518" type="event" subtype="system" level="information" vd="root" logdesc="LTE modem active SIM card switch event" msg="LTE modem active SIM card slot changed to 2 by user."

Example 2

In this section, automatic SIM card switching is enabled and configured to switch based on SIM state, connection state, or link monitor state, and it includes example event logs for each scenario.

To enable automatic SIM card switching by SIM state:

1. Enable automatic SIM card switching by SIM state:

   config system lte-modem
       config sim-switch
           set by-sim-state enable
       end
   end

   With this configuration, the second SIM card becomes active when the active SIM card is no longer detected, for example, if the active SIM card is ejected. The following event logs are generated:

   5: date=2023-04-28 time=17:27:27 eventtime=1682728046989682780 tz="-0700" logid="0100046513" type="event" subtype="system" level="information" vd="root" logdesc="LTE modem data link connection event" msg="LTE modem data link changed from QMI_WDS_CONNECTION_STATUS_DISCONNECTED to QMI_WDS_CONNECTION_STATUS_CONNECTED"
   
   6: date=2023-04-28 time=17:27:17 eventtime=1682728036493684280 tz="-0700" logid="0100046512" type="event" subtype="system" level="information" vd="root" logdesc="LTE modem SIM card state event" msg="LTE modem SIM card change from QMI_UIM_CARD_STATE_ABSENT to QMI_UIM_CARD_STATE_PRESENT"
   
   7: date=2023-04-28 time=17:27:12 eventtime=1682728032589776580 tz="-0700" logid="0100046513" type="event" subtype="system" level="information" vd="root" logdesc="LTE modem data link connection event" msg="LTE modem data link changed from QMI_WDS_CONNECTION_STATUS_CONNECTED to QMI_WDS_CONNECTION_STATUS_DISCONNECTED"
   
   8: date=2023-04-28 time=17:27:11 eventtime=1682728031245682560 tz="-0700" logid="0100046512" type="event" subtype="system" level="information" vd="root" logdesc="LTE modem SIM card state event" msg="LTE modem SIM card change from QMI_UIM_CARD_STATE_PRESENT to QMI_UIM_CARD_STATE_ABSENT"

To enable automatic SIM card switching by connection state:

1. Enable automatic SIM card switching by connection state:

   config system lte-modem
       config sim-switch
           set by-connection-state enable
           set modem-disconnection-time 30
           set sim-switch-log-alert-interval 15
           set sim-switch-log-alert-threshold 5
       end
   end

   With this configuration, the second SIM card becomes active when the modem cannot establish a connection with the carrier through the active SIM card. For example, a FortiGate is in a room with poor signal quality. With this configuration, the SIM card switch is triggered after the modem is detected as disconnected for 30 seconds, and the following event log is generated:

   56: date=2023-05-01 time=11:14:56 eventtime=1682964896356933480 tz="-0700" logid="0100046519" type="event" subtype="system" level="notice" vd="root" logdesc="LTE modem active SIM card switched: modem disconnection detected" msg="LTE modem active SIM card slot changed to 2, due to modem connection down."
   
   66: date=2023-05-01 time=11:14:13 eventtime=1682964852964869400 tz="-0700" logid="0100046519" type="event" subtype="system" level="notice" vd="root" logdesc="LTE modem active SIM card switched: modem disconnection detected" msg="LTE modem active SIM card slot changed to 1, due to modem connection down."
   

   When poor signal quality causes SIM cards to frequently switch back and forth, and the flapping rate occurs more than five times within the configured 15 minute time period, an event log is triggered to record the flapping severity:

   65: date=2023-05-01 time=11:14:13 eventtime=1682964853083194400 tz="-0700" logid="0100046521" type="event" subtype="system" level="warning" vd="root" logdesc="LTE modem active SIM card slot flipped back and forth in short time" msg="LTE modem switched SIM slot 8 times in last 15 minutes, which is greater than 5 times threshold."

To enable automatic SIM card switching based on link monitor:

1. Enable automatic SIM card switching by link monitor, and specify the link monitor:

   config system lte-modem
       config sim-switch
           set by-link-monitor enable
           set link-monitor "modem"
           set sim-switch-log-alert-interval 15
           set sim-switch-log-alert-threshold 5
       end
       config system link-monitor
       edit "modem"
           set srcintf "wwan"
           set server "8.8.8.8"
           set interval 1000
           set probe-timeout 100
           set failtime 3
           set recoverytime 8
       next
   end

   With this configuration, the second SIM card becomes active when the link monitor detects the active SIM card exceeds the SLA.

2. Check the link monitor status. In this example, the link monitor status is dead:

   # diagnose system link-monitor status modem
   
   Link Monitor: modem, Status: dead, Server num(1), cfg_version=7 HA state: local(dead), shared(dead)
   Flags=0x9 init log_downgateway, Create time: Fri Apr 28 16:34:56 2023
   Source interface: wwan (19)
   VRF: 0
   Interval: 1000 ms
   Service-detect: disable
   Diffservcode: 000000
   Class-ID: 0
     Peer: 8.8.8.8(8.8.8.8) 
           Source IP(10.192.195.164)
           Route: 10.192.195.164->8.8.8.8/32, gwy(10.192.195.165)
           protocol: ping, state: dead
                   Packet lost: 11.667%
                   MOS: 4.353
                   Number of out-of-sequence packets: 0
                   Recovery times(5/8) Fail Times(1/3)
                   Packet sent: 60, received: 56, Sequence(sent/rcvd/exp): 61/61/62

   The following event log is generated when the link-monitor status is dead:

   15: date=2023-04-28 time=16:31:38 eventtime=1682724697936494139 tz="-0700" logid="0100046520" type="event" subtype="system" level="notice" vd="root" logdesc="LTE modem active SIM card switched: link monitor probe failure detected" msg="LTE modem active SIM card slot changed to 2, due to link monitor probe failures."
   
   19: date=2023-04-28 time=16:31:13 eventtime=1682724673152506599 tz="-0700" logid="0100022932" type="event" subtype="system" level="warning" vd="root" logdesc="Link monitor status warning" name="modem" interface="wwan" probeproto="ping" msg="Link Monitor changed state from alive to dead, protocol: ping."