Failing to netboot Mikrotik RB760iGS (hEX S) with OpenWrt

[abhocetabhac]

Hi, guys.

Over the years I have flashed OpenWRT into many routers. Recently, I bought
my first Mikrotik (an hEX S RB760iGS) and I am having a hard time trying to
netboot OpenWRT. As prescribed in the wikis, through the web interface, I set:

System → Routerboard → Settings → Boot device: Try ethernet once then NAND
System → Routerboard → Settings → Boot protocol: DHCP
System → Routerboard → Settings → Force Backup Booter

and shut the router down. Whence, I run on my machine:

sudo dnsmasq --user=abhocetabhac --no-daemon -i enp0s20f0u2u2 --listen-address 192.168.2.10 --bind-interfaces -p0 --dhcp-authoritative --dhcp-range=192.168.2.50,192.168.2.100 --bootp-dynamic --dhcp-boot=openwrt-21.02.1-ramips-mt7621-mikrotik_routerboard-760igs-initramfs-kernel.bin --log-dhcp --enable-tftp --tftp-root=/tmp

But, when I turn the router back on, it looks like the bootloader downloads the image file dozens of times for a minute or so. Then, after a number of tries, it aborts and reboots the router with RouterOS from flash memory.

Any help would be direly appreciated, please.

[frollic]

Check if this might apply to your device too

MikroTik hEX RB750Gr3 boot issue

Problem solved! Thank you to u/Bradmck over at Reddit for the resolution. For anyone that has a newer version of this board: Load RouterOS 6.49.2 and then follow the install instructions on https://openwrt.org/toh/mikrotik/rb750gr3 All versions prior to this does not work (I only tried 7.1.1 after that version and it does not work either). This worked for me and I hope that it will work for you

[abhocetabhac]

Thank you, u/frolic. I tried the upgrade but it did not work. Methinks, upgrading does not touch the boot loader.

Nevertheless, I finally managed to flash OpenWRT departing from the instructions in the Wiki in two fundamental ways. The DHCP client of the boot loader seems to be broken, so I used BOOTP. There was no way to make it work in DHCP netboot mode. Secondly, instead of dnsmasq, I resorted to TFTP-HPA and standard ISC DHCP implementations.

The procedure is as follows:

# I use Void linux, but Debian is similar (packages tftp-hpa and isc-dhcp).
sudo xbps-install -Su tftp-hpa dhcp

sudo ip addr flush dev enp0s20f0u2u2
sudo ip addr add 192.168.88.2/24 dev enp0s20f0u2u2
sudo ip link set enp0s20f0u2u2 up

# Find out the MAC address of the Wan port of the router.
# Enter the RouterOS terminal and execute the command
#   "/interface ethernet print"
# Take note of the MAC address of interface "ether1":
# "08:55:31:aa:bb:e4".

# Log into the web interface of RouterOS and set router to boot from 
# ethernet once and with BOOTP:
#    System → Routerboard → Settings → Boot device: Try ethernet once then NAND
#    System → Routerboard → Settings → Boot protocol: BOOTP
#    System → Routerboard → Settings → Force Backup Booter: Checked
#                                      (if supported by your routerboard - !IMPORTANT)
#    System → Shutdown
# Pull off the router's power cord.
#
# CAVEAT: Contrary to what is incentivized in the wiki, the boot protocol set through
#         the RouterOS's web interface must be "BOOTP", instead of "DHCP".

# Set the stage for the TFTP server.

sudo mkdir -p -m 1777 /tmp/tftpd

sudo cp ~/pathto/openwrt-21.02.1-ramips-mt7621-mikrotik_routerboard-760igs-initramfs-kernel.bin /tmp/tftpd/openwrt.bin
sudo chmod 0777 /tmp/tftpd/*

# Set the stage for the DHCP/BOOTP server.

sudo mkdir -p -m 1777 /tmp/dhcpd

sudo bash -c 'cat > /tmp/dhcpd/dhcpd.conf << _EOF
subnet 10.1.1.0 netmask 255.255.255.0 {
    range 10.1.1.100 10.1.1.110;
    default-lease-time 600;
    max-lease-time 7200;
    option subnet-mask 255.255.255.0;
    option broadcast-address 10.1.1.255;
    option routers 10.1.1.1;
    option domain-name-servers 10.1.1.2;
    option domain-name "mikrotik2openwrt.io";
    authoritative;
}

#allow bootp;

host mikrotik {
    hardware ethernet 08:55:31:aa:bb:e4;
    fixed-address 10.1.1.1;
    filename "openwrt.bin";
    option domain-name-servers 10.1.1.2;
    option domain-name "mikrotik2openwrt.io";
}
_EOF'

sudo touch /tmp/dhcpd/dhcpd.leases

# Test the DHCPd configuration file.
sudo dhcpd -f -d -cf /tmp/dhcpd/dhcpd.conf -lf /tmp/dhcpd/dhcpd.leases -t

# Run the TFTP and DHCP servers.

sudo ip addr flush dev enp0s20f0u2u2
sudo ip addr add 10.1.1.2/24 dev enp0s20f0u2u2
sudo ip link set enp0s20f0u2u2 up

# On a terminal, execute:
sudo in.tftpd -v -L -s -a 10.1.1.2:69 /tmp/tftpd

# And, on a second terminal, run:
sudo dhcpd -f -d -cf /tmp/dhcpd/dhcpd.conf -lf /tmp/dhcpd/dhcpd.leases 

# Connect the cable to the WAN port and turn the router on.

# Watch the DHCP server output as the bootloader fetches the IP address.

# Wait until the DHCP server starts reporting successive requests again and
# the blue LED on the router stops blinking.
# The router should now be running OpenWRT from RAM. 

# Press Ctrl-C to finish both daemons.

sudo ip addr flush dev enp0s20f0u2u2
sudo ip addr add 192.168.1.2/24 dev enp0s20f0u2u2

# Disconnect the cable from the WAN port and plug it into a LAN port.

ping 192.168.1.1

# Access the OpenWRT web interface and navigate to 
#     System -> Backup/Flash Firmware
# Finally, flash the sysupgrade image file:
# "~/pathto/openwrt-21.02.1-ramips-mt7621-mikrotik_routerboard-760igs-squashfs-sysupgrade.bin".