Guidelines on Flashing OpenWRT on a Mikrotik Machine via a VM

This guide takes inspiration from OpenWRT Mikrotik Guide.

Prerequisites

• Nix Package Manager (optional but recommended)
• Vagrant or any other VM software

If you're using NixOS like I am, and want to follow this guide without changing your distribution, consider installing the Nix package manager from here.

Flash Guide

1. Create a Directory for TFTP Server

   mkdir ~/tftpserver/
   cd ~/tftpserver/
   mkdir srv/

2. Prepare Boot Files

   Place the boot files for your specific router in the srv/ directory. Connect your Ethernet cable to port 1 of your router and the other end to your host machine. Access your router via WinBox or your browser, and navigate to System -> RouterBoot -> Settings. Change the following setting:

   • Boot method: DHCP (optional as dnsmasq supports bootp as well)

   Note: If you can't access the router via WinBox through the eth1 port, try connecting the cable to port 2. However, the flash will only work through port 1.

3. Initialize a Vagrant VM

   cd ~/tftpserver/
   vagrant init alpine/alpine64

   Edit the generated Vagrantfile to include the following line, ensuring the VM is on the same subnet as the router:

   config.vm.network "public_network", dev: "network_interface_placeholder"

   Replace network_interface_placeholder with the network interface of the Ethernet connection associated with your router.

4. Boot and Access the VM

   vagrant up
   vagrant ssh

   Change the root password in your VM:

   sudo passwd root

5. Transfer Boot Files to the VM

   From your host machine, transfer the initramfs file to the VM:

   scp tftpserver/srv/openwrt-23.05.0-ath79-mikrotik-mikrotik_routerboard-951ui-2nd-*.bin vagrant@192.168.121.*:/home/vagrant/

6. Install and Configure dnsmasq

   sudo apk update
   sudo apk add dnsmasq
   which dnsmasq

7. Create and Execute loader.sh Script

   Create a script named loader.sh with the following content:

   #!/bin/bash
   IFNAME=eth1
   /sbin/ip addr replace 192.168.88.10/24 dev $IFNAME
   /sbin/ip link set dev $IFNAME up
   /usr/sbin/dnsmasq \
     --no-daemon \
     --listen-address 192.168.88.10 \
     --bind-interfaces \
     -p0 \
     --dhcp-authoritative \
     --dhcp-range=192.168.88.100,192.168.88.200 \
     --bootp-dynamic \
     --dhcp-boot=/home/vagrant/openwrt-19.07-*-initramfs-* \
     --log-dhcp \
     --enable-tftp \
     --tftp-root=/home/vagrant/

   Ensure the script is executable and the initramfs file has the correct permissions:

   chmod +x loader.sh
   chmod 644 /home/vagrant/openwrt-23.05.0-ath79-mikrotik-mikrotik_routerboard-951ui-2nd-*.bin

   Run the TFTP server:

   su
   ./loader.sh

8. Boot the Router into OpenWRT

   Power off the router, press the reset button, and hold it while powering it back on for 15-20 seconds or until logs appear in the VM terminal. Your router should boot into OpenWRT. On rebooting, it will revert to RouterOS.

   Note: Access OpenWRT via your browser at http://192.168.1.1/.

Debugging Steps

If the router isn't accessible via WinBox or your browser, try the following:

• Change the IP address attached to the network interface of your router's Ethernet connection to one in the same network as the router. NixOS users can add this to their configuration.nix:

  networking.firewall.enable = false;
  networking.interfaces.<network_interface_placeholder> = {
    ipv4.addresses = [
      {
        address = "192.168.88.x";
        prefixLength = 24;
      }
    ];
    useDHCP = true;
  };

If the router remains inaccessible, power it off, hold the reset button for 15-20 seconds while powering it back on. Access the router configuration page via WinBox or your browser, and go to System -> Reset Configuration to reset the router to the default RouterOS configuration.