Radio channel and Cellular (LTE) combination


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4. Radio channel and Cellular (LTE) combination

Example 4 – Radio channel and Cellular LTE combination

Fig. 4.1: Example 4 – Radio channel and Cellular LTE combination

4.1. Description

Example 4 depicts a situation with two RipEX2 units equipped with LTE module. Both units are connected to the private APN and GRE tunnel is built between them to enable mutual communication over the cellular network.


Check M!DGE2 application notes and manual for more details about cellular networks and APN explanations.

This cellular path will be set with Rx cost equal to 50 to be better than RF channel, but worse than Ethernet connection. It can resemble Wired networks, but we will use Wireless. Choose whatever fits you more in your particular installation.

The example uses the Example 2 configuration as a startup point.

4.2. RipEX_B Configuration


Keep in mind we set up RACOM private APN. Your APN setup and IPs will be different! Make appropriate changes so that your configuration reflects your APN details.

Enable the cellular interface.

RipEX_B – Cellular interface

Fig. 4.2: RipEX_B – Cellular interface

You can keep everything in defaults, but set it as required by you and the cellular operator.

Configure your APN details in SIM1 panel.

RipEX_B – SIM1 setup

Fig. 4.3: RipEX_B – SIM1 setup

Create a GRE tunnel interface.

RipEX_B – GRE tunnel over cellular network

Fig. 4.4: RipEX_B – GRE tunnel over cellular network

The Peer IP address is the IP of the RipEX_D cellular interface. Tunnel address/mask is a new setup for GRE tunnel addresses.

The last step is configuring Babel Network interface again. Add a new interface.

RipEX_B – Babel interface (GRE over LTE)

Fig. 4.5: RipEX_B – Babel interface (GRE over LTE)

Note the cellular interface is called “aux”, but we need to define a GRE interface. Its name is “gre_tun0”. Change the Type to “Wireless” and set the Rx cost to 50. The Hello interval parameter is increased from 4 to 10. It is still faster than over RF channel (30 seconds), but not so fast as via Ethernet (4 seconds). Optimize this number to suit your needs and possible data usage of your SIM cards.

The Advertised next hop is its local GRE IP address.

Do not forget to set a new static route over cellular/aux network. A new route should either be a default one, or like with our example, we route there APN’s subnet Go to the SETTINGS – Routing – Static menu and add a new rule.

RipEX_B – Static routing via cellular (aux) interface

Fig. 4.6: RipEX_B – Static routing via cellular (aux) interface

Note that you can make this cellular/LTE routing rule permanent causing that if LTE is down, the rule is still active and traffic for LTE segment is not handled by another Routing rule (unreachable messages). Once LTE comes up again, the routing rule works as expected again.

To do so, check “Routing_Persistent” parameter in this routing rule. Save the changes.

4.3. RipEX_D Configuration

Common settings are the same. In your APN, you might have a different SIM1 setup compared to RipEX_B (each SIM can have different Authentication credentials).

Once the cellular interface is ready, create a new GRE tunnel setup again.

RipEX_D – GRE tunnel setup

Fig. 4.7: RipEX_D – GRE tunnel setup

Peer address is the cellular IP of RipEX_B; is a new local GRE IP address.

Add a new Babel Network interface.

RipEX_D – Babel interface (GRE over LTE)

Fig. 4.8: RipEX_D – Babel interface (GRE over LTE)

Add a new static route via a cellular interface.

RipEX_D – Static routing via cellular (aux) interface

Fig. 4.9: RipEX_D – Static routing via cellular (aux) interface

You can make the rule persistent again.

Save the changes.

4.4. Diagnostics and Testing

Check the Cellular/LTE status in SETTINGS – Interfaces – Cellular menu.

RipEX_B – Cellular interface status

Fig. 4.10: RipEX_B – Cellular interface status

The status provides with a lot of information about current cellular connection.

Now, go to the Diagnostics and Tools menu. Try the mutual ping between and Also run a ping between and IP addresses.

RipEX_B – Pings over cellular/LTE

Fig. 4.11: RipEX_B – Pings over cellular/LTE

If these pings are not working correctly, check your APN setup and GRE tunnel configuration.

Go to the Diagnostics – Routing menu and check the Babel statistics.

RipEX_B – Babel Routing

Fig. 4.12: RipEX_B – Babel Routing

There are already 3 routes to each destination in RipEX_B radio. Two are using RF channel and one the GRE tunnel. Cost/Metric via LTE is set to “50” so you can see a route to via “gre_tun0” with a Metric equal to 50.

You can test the scenario by unplugging the cellular antennas or turning off RipEX_B completely. Keep the ICMP ping running from your laptop to IP address again.

Check Statistics and Monitoring menus. It is NOT possible to monitor cellular interface in RipEX2 firmware and older. Also note that Monitoring via Remote access is only available since RipEX2 firmware

RipEX_A – neighbors (cellular antenna removed from RipEX_B)

Fig. 4.13: RipEX_A – neighbors (cellular antenna removed from RipEX_B)

You can also check if the cellular interface is “up” or “down” in the SETTINGS – Interfaces – Cellular menu.

RipEX_B – Cellular/LTE connection down

Fig. 4.14: RipEX_B – Cellular/LTE connection down

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