MikroTik RB921 Series

This page covers the MikroTik RouterBoard921-series, which is a stripped down version of the RouterBoard 922. MikroTik uses this board as base for some other products, like

• mANTBox 15s (https://mikrotik.com/product/RB921GS-5HPacD-15S)
• mANTBox 19s (https://mikrotik.com/product/RB921GS-5HPacD-19S)
• NetMetal 5SHP (https://mikrotik.com/product/RB921UAGS-5SHPacD-NM)
• NetMetal 5SHP triple (https://mikrotik.com/product/RB921UAGS-5SHPacT-NM)

The board has QCA9557 @ 720MHz; 128MB RAM; 128MB NAND, 64kB config-NOR; 1G Lan-port; QCA9892 5GHz a/n/ac. The concrete antenna differs on the final model.

On the right-side of the pcb is still the printing “RB922GS 5HPac”, which shows the origin of the design. A bit above is the not populated MiniPCI-e socket, on the lower right end is the unpopulated USB-connector.

→ See the MikroTik Common Procedures for specific instructions.

For full documentation have a look at Common Procedures for Mikrotik RouterBoard Products

How you install OpenWrt, using Mikrotik mANTBox 15s as example:

1. You need a DHCP server because the device is using DHCP to get the first IP. You can use dnsmasq (see below) for this task. Start DHCP server and do the following:
   1. boot Mikrotik Routerboard. Search the IP of the device in DHCP server log. Log into web interface with user: “admin” and empty password
   2. System → Routerboard → Settings → Boot device: Try ethernet once then NAND. This configuration is only valid for the next reboot. This means that you need to activate this again if you your first try to install OpenWRT was not successful.
   3. System → Routerboard → Settings → Boot protocol: DHCP
   4. System → Routerboard → Settings → Force Backup Booter: Checked (if supported by your routerboard - !IMPORTANT)
   5. System → shutdown (NO reboot)
2. Start DHCP server and TFTP server (if not already done):
   1. configure fix IP for TFTP server, e.g. 192.168.1.2
   2. download ramfs images. Copy images to e.g. /srv/tftp
      1. initramfs: https://downloads.openwrt.org/releases/19.07.4/targets/ar71xx/mikrotik/openwrt-19.07.4-ar71xx-mikrotik-vmlinux-initramfs.elf
   3. start dnsmasq with the following command (replace enp0s25 with your network adapter)

       dnsmasq -i enp0s25 --dhcp-range=192.168.1.100,192.168.1.200 --dhcp-boot=openwrt-19.07.4-ar71xx-mikrotik-vmlinux-initramfs.elf --enable-tftp --tftp-root=/srv/tftp/ -d -u age -p0 -K --log-dhcp --bootp-dynamic

   4. start mANTBox
      1. if you see in dnsmasq log that vmlinux-initramfs.elf image was send to 192.168.1…. then mANTBox is booting OpenWRT
      2. wait for one/two minutes…
      3. on the Mikrotik device a non-persistent firmware is installed. You can now access the web interface of OpenWRT. Note: If you do reboot the device now the original Mikrotik firmware is booted!
   5. Connect to newly flashed OpenWRT (via web interface or ssh)
   6. Install the final persistent firmware now via OpenWRT tools (e.g. upload https://downloads.openwrt.org/releases/19.07.4/targets/ar71xx/mikrotik/openwrt-19.07.4-ar71xx-mikrotik-nand-large-ac-squashfs-sysupgrade.bin )
   7. Device should reboot automatically.
   8. Done.

→ generic.sysupgrade

cd /tmp
wget http://downloads.openwrt.org/snapshots/trunk/XXX/xxx.abc
sysupgrade /tmp/xxx.abc

cd /tmp
wget http://downloads.openwrt.org/snapshots/trunk/XXX/xxx.abc
mtd write /tmp/xxx.abc linux && reboot

→ generic.debrick

→ failsafe_and_factory_reset

→ Basic configuration After flashing, proceed with this.
Set up your Internet connection, configure wireless, configure USB port, etc.

→ hardware.button on howto use and configure the hardware button(s). Here, we merely name the buttons, so we can use them in the above Howto.

This seems in fact a RB921 board combined with the MikroTik mANT 15s sector-antenna.

Front:

Back:

Backside label:
Insert photo of backside label

Note: This will void your warranty!

Unscrew the 8 screws visible on the back with a T9 screwdriver.

Main PCB:
Insert photo of PCB

→ port.serial general information about the serial port, serial port cable, etc.

How to connect to the Serial Port of this specific device:
Insert photo of PCB with markings for serial port

→ port.jtag general information about the JTAG port, JTAG cable, etc.

How to connect to the JTAG Port of this specific device:
Insert photo of PCB with markings for JTAG port

→ bootloader

Space for additional notes, links to forum threads or other resources.

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