• Mikrotik is a very popular supplier of networking equipment.
• They have their own operating system called RouterOS which most probably is Linux based.
• RouterOS however is licensed and includes different levels of licensing for different functionalities.
• To unlock a needed feature not included with the current license then requires you to upgrade which obviously involves cost.
• However, the hardware itself is good and durable and it is easy to source all over the world.
• Some of their models are also able to run OpenWRT as an alternative to RouterOS.
• OpenWRT is OpenSource and there is no paid for licensing involved on OpenWRT.
• This page will just cover the flash from RouterOS to OpenWRT.
• We will cover the configuration of the device once OpenWRT is running on it on a separate page.

• Linux based machine to communicate with the Mikrotik and supply the OpenWRT firmware over the network.
• Mikrotik RB750Gr3 reset to factory defaults
• 1xCat5 LAN cable.

• The flash process is fairly simple and straight forward and involves three steps
  1. Export the RouterOS License Key.
  2. Load a RAM based version of OpenWRT.
  3. Flash the permanent (Flash) version of OpenWRT using the RAM based version.

• It is recommended that you export the RouterOS license key in the event of returning to the original RouterOS, you might need to use it again to activate the RouterOS.
• RouterOS can be accesses various ways which include
  • Web based UI called Webfig (default http://192.168.88.1) on the LAN side of the board
  • Using the WinBox application.
• Unfortunately the Webfig interface does not support the export of the license key. (Only upgrade)
• We have to use WinBox for that.

• WinBox is a windows based program but since its a simple program its just as easy to run it on Ubuntu using Wine.
• We assume you have a standard install of Ubuntu 20.04 (with some GUI)
• Install Wine

sudo apt-get install wine

• Download the latest version of Winbox from Mikrotik
• https://mikrotik.com/download
• Use Wine to run winbox64.exe

#cd to where the winbox64.exe program is
wine winbox64.exe

• Configure the LAN port of your Ubuntu machine to have an IP Address on the 192.168.88 subnet.

#Here our LAN interface is enp8s0 
#Use ip a to discover what it is caleld on your machine
sudo ip addr add 192.168.88.10/24 dev enp8s0

• Use the LAN cable to connect to any of the LAN ports on the Mikrotik (2-5) to your Ubuntu machine.
• Go to the Neighbors tab and see if the device is listed.
• Click on the listed device and click Connect to enter into its configuration.
• Select System → License
• Click on Export Key to export it.
• Store it on a safe place

Now that we have the license key taken care of we can go to the next step which is to load the RAM based OpenWRT onto the device

• In order for us to get the RAM based version of OpenWRT onto the Mikrotik two things are involved.
  1. There has to be a BOOTP environment set up to serve the RAM based image
  2. The Mikrotik has to be set in such a mode as to use the BOOTP environment to fetch the RAM based image using BOOTP
• On Ubuntu it is very simple and we just create a small shell script to take care of it

loader.sh

#!/bin/bash
USER=system
IFNAME=enp8s0
/sbin/ip addr replace 192.168.1.10/24 dev $IFNAME
/sbin/ip link set dev $IFNAME up
/usr/sbin/dnsmasq --user=$USER \
--no-daemon \
--listen-address 192.168.1.10 \
--bind-interfaces \
-p0 \
--dhcp-authoritative \
--dhcp-range=192.168.1.100,192.168.1.200 \
--bootp-dynamic \
--dhcp-boot=openwrt-19.07.6-ramips-mt7621-mikrotik_rb750gr3-initramfs-kernel.bin \
--log-dhcp \
--enable-tftp \
--tftp-root=$(pwd)

• As you can see we will serve the openwrt-19.07.6-ramips-mt7621-mikrotik_rb750gr3-initramfs-kernel.bin image to the Mikrotik.
• Download this image (This was the latest 19.07 based image at the time of this writing)
• Make sure it is located in the same directory as the loader.sh script.
• Do the following to start up the BOOTP service

<code bash>

</code<