X. WAN

This article demonstrates when and how to setup LTE bridge mode based on DrayTek Vigor 2620Ln router.

You may come across a situation where an additional LTE connection is needed as a backup for a router in your data centre. Most of the comms rooms are in a location with a very weak or no LTE signal. A typical scenario is shown in the diagram below. A USB LTE modem is attached to the broadband router for the backup WAN connection but since the LTE signal is non-existent, it will not be possible to use this option.

One option is to attach an external aerial to the modem, but it requires a long coax cable run to the aerial mounted outside the building. For long cable runs, the losses incurred in the cable will negate any gains from the antenna. Therefore, making this an ineffective solution.

Proposed Solution

The proposed solution is to install an external LTE bridge modem located in the area with a strong LTE signal and connect it to the broadband router in the data centre by UTP cable, which can be up to 100 meters long as shown in the diagram below. This solution will provide a reliable LTE WAN connection with no loss of signal to the LTE modem.

DrayTek Solution

The solution here is to use the DrayTek Vigor 2620Ln router. This router has the option to configure it as a bridged LTE modem. The LAN port of the router is then connected to the WAN port of the broadband router in the data centre.

The Vigor 2620Ln has an unlocked integrated LTE modem that accepts standard-sized SIM cards from major service providers. This router has two SIM card slots. A SIM card from a different service provider can be installed simultaneously to provide failover if the primary LTE connection goes down.

The diagram below shows the network topology where we have a Vigor2620Ln configured in bridge mode. A UTP cable is used to connect the LAN port of the Vigor2620Ln to the Ethernet WAN port of the broadband router. The Vigor2620Ln can be placed next to a window or other suitable locations that have a strong LTE signal. As mentioned previously, the UTP cable can be up to 100 meters long, so structured cabling within the building can be utilized for the connection.

Since the LTE router (Vigor2620Ln) will become transparent when in bridge mode, the attached broadband router will need to provide authentication if required. Usually, only DHCP client needs to be enabled in the broadband router's WAN configuration.