The Goal

This article explains how to properly configure your Openwrt based router to work with Mikrotik antenna like this or this with LTE pass through feature enabled.

Background

I had a typical setup for my home router. Home network + wan internet via 3g stick.

Later I've decided to replace 3g stick to LTE antenna to gain all benefits of LTE high speed and now my setup looks like this.

The problem

When I bought and configured Mikrotik antenna it turned out that it is a boarder device now, not router anymore.
So I have to configure all the stuff like firewall/port forwarding/traffic rules/security on the Mikrotik device.
That is annoying and not convenient.

I just want my Mikrotik antenna to act like my old 3g stick plugged into my router. Simple radio signal receiver not a separate network device that has a complex configuration.

Luckily, Mikrotik shipped new version of Router OS v6.41 with the feature calls LTE passthrough.

It means that Mikrotik device passes through WAN IP obtained from internet provided to Openwrt based router, and we do all configuration/firewalling/security on the router as we did before and don't need to deal with all the configuration burden in the Mikrotik Router OS anymore.

Solution

All instructions provided here was tested against Mikrotik antenna LHG LTE6 kit (Router OS 6.49) and router TP-Link Archer C7 v2 (openwrt 19.07).
For Router OS configuration I use Winbox tool.

On the Openwrt side

Step 1: Configure two VLAN's to negotiate with Mikrotik device

• Network -> Switch
• Enable VLAN functionality
• Add 2 VLAN's as shown on the picture bellow
• VLAN 2 untagged (management VLAN)
• VLAN 3 tagged (internet VLAN)
• Click Save & Apply

Step 2: Configure interface on top of management VLAN

• Network -> Interfaces -> Add new interface
• Name: whatever you want
• Protocol: Static address
• Interface: Switch VLAN: "eth0.2"
• Click "Create Interface"
• IPv4 address: IP from your Mikrotik network range (in my case 192.168.100.2, because Mikrotik itself has ip 192.168.100.1)
• IPv4 netmask: 255.255.255.0
• Click "Save"
• Click "Save & Apply"

Step 3: Configure interface on top of internet VLAN

• Network -> Interfaces -> Add new interface
• Name: whatever you want (in my case WAN)
• Protocol: DHCP client
• Interface: Switch VLAN: "eth0.3"
• Click "Create Interface"
• Check "Bring up on boot"
• REMEMBER MAC ADDRESS FROM THIS STEP
• Click "Save"
• Click "Save & Apply"

On the Mikrotik side

Step 1: Create management VLAN on your ether1 interface

• Interfaces -> Interface (tab) -> select ether1 -> Click big plus -> VLAN
• Name: whatever you want
• VLAN ID: 2
• Interface: ether1
• Click OK

Step 2: Create internet VLAN on your ether1 interface

• Interfaces -> Interface (tab) -> select ether1 -> Click big plus -> VLAN
• Name: whatever you want
• VLAN ID: 3
• Interface: ether1
• Click OK

Step 3: Enable pass through for your internet VLAN

• Interfaces -> LTE (tab) -> select lte1 -> Click LTE APNs -> double-click default
• Passthrough interface: name from step 2 (in my case vlan-3-internet)
• Passthr. MAC address: mac address from step 3 on the openwrt side
• Click OK

If you did all the steps correctly, Mikrotik should get WAN IP from your internet provider and assign it to your openwrt WAN interface.

Enjoy ! :)