Monday, May 14, 2012

Installing OpenWRT on a RouterBOARD 750GL

I have a project that requires a small Linux router/firewall, with a requirement of no wireless (due to physical security policies for the site). There are many third-party firmware options for wireless routers, with distributions such as dd-wrt and Open-WRT on APs from Linksys, Buffalo, etc. But the options for a simple wired router are more limited.

I found this excellent post: OpenWRT on Mikrotik Routerboard 411/750 on Wolfs Tech Blog, which indicated that OpenWRT is flashable onto a RouterBoard 750GL. I bought a pair from They were $59.95 each via Google Checkout, and shipping was fast.

I highly recommend great service!

The RouterBOARD 750GL has 5 gigabit ports, 64MB of SDRAM, 64MB NAND, and it literally fits in the palm of your hand.
RouterBOARDs ship with a proprietary RouterOS, but my project requires Linux.

I used the Wolfs Tech Blog post as my guide for installation, with help from this German post, with an assist from Google Translate. I ran into a few gotchas, so I thought I'd save someone else future grief and post my step-by-step instructions. Firmware installation can be tricky: there is no serial or display port on the 750GL: you need to "fly blind" and install over the network.

I used Xubuntu 12.4 as the OS for building OpenWRT, and as the TFTP/DHCP server to boot the RouterBoard via the network. I initially tried using a VMWare Workstation guest, but later encountered problems making the DHCP server work properly via a bridged interface. I ended up installing to USB, booted off the USB, and ran Xubuntu natively.

Install the required packages and Wireshark (which will be handy later):
$ sudo apt-get install subversion
$ sudo apt-get install g++ gawk libncurses5-dev zlib1g-dev git-core
$ sudo apt-get install dhcp3-server atftpd apache2
$ sudo apt-get install wireshark
Download the OpenWRT trunk code with Subversion and "make menuconfig":
$ cd
$ mkdir openwrt
$ cd openwrt
$ svn co svn://
$ cd trunk
$ make menuconfig
We need to compile twice. Once for the .tar.gz file, and once for the ramdisk.  Two steps because the .tar.gz file has has different requirements than the ramdisk, such as squashfs.

First the tar.gz file:

  • Target System: Atheros AR7xxx/AR9xxx 
  • Subtarget: (Devices with NAND flash (mostly Mikrotik)) 
  • Target Images: .tar.gz
Exit and type "make". It will take a long time to compile.

When complete, type the following:
$ cp ~/openwrt/trunk/bin/ar71xx/openwrt-ar71xx-nand-vmlinux-initramfs.elf /var/www
$ cp ~/openwrt/trunk/bin/ar71xx/openwrt-ar71xx-nand-rootfs.tar.gz /var/www
This prepares them for the "wget2nand" flashing step, coming up later.

Next the ramdisk:
$ cd ~/openwrt/trunk
$ make clean
$ make menuconfig
  • Target System: Atheros AR7xxx/AR9xxx 
  • Subtarget: (Devices with NAND flash (mostly Mikrotik)) 
  • Target Images: ramdisk
Exit and type "make". 

When complete copy the ramdisk to /srv/tftp:
$ cp ~/openwrt/trunk/bin/ar71xx/openwrt-ar71xx-nand-vmlinux-initramfs.elf /srv/tftp/
Configure atftpd and isc-dhcp-server. I used as the TFTP server address, and assigned to the RouterBoard. Avoid (the default OpenWRT IP address).

Edit /etc/network/interfaces, use as a static IP address:
auto eth0
iface eth0 inet static
Edit /etc/default/atftpd, changes in bold:
OPTIONS="--bind-address --tftpd-timeout 300 --retry-timeout 5 --mcast-port 1758 --mcast-addr --mcast-ttl 1 --maxthread 100 --verbose=5 /srv/tftp"
Locate the first MAC address printed on the bottom of the RouterBOARD 750GL:
Edit /etc/dhcp/dhcpd.conf, and use the first listed MAC address as the hardware ethernet address:
allow booting;
allow bootp;
one-lease-per-client true;

subnet netmask {
  option routers;
  option subnet-mask;
  option broadcast-address;
  ignore client-updates;

group {
  host routerboard {
    hardware ethernet 00:0c:42:aa:bb:cc;
    filename "openwrt-ar71xx-nand-vmlinux-initramfs.elf";
Now restart networking, atftpd and isc-dhcp-server:
$ sudo /etc/init.d/networking restart
$ sudo /etc/init.d/atftpd restart
$ sudo /etc/init.d/isc-dhcp-server restart
Run Wireshark, sniffing on eth0, to watch network traffic.

Boot the RouterBOARD 750GL via TFTP:
  • Connect an ethernet cable between port 1 on the RouterBOARD 750GL and the TFTP server.
    • Other ports won't work 
  • Press the small "RES" button and plug in the power cable. 
  • The "PWR" and "ACT" lights will illuminate. Then "ACT" will flash, and finally stop. 
  • Now release the "RES" button. 
  • The 750GL should request a DHCP address, receive, download openwrt-ar71xx-nand-vmlinux-initramfs.elf via TFTP, and boot OpenWRT. 
Use Wireshark to ensure everything's working; look for the TFTP "DATA Packet" packets to verify the ramdisk download.
The device will boot OpenWRT and use IP address

Swap the cable to a different port to access OpenWRT. I used port 2 (port 1 won't work). Then telnet to the device:
$ telnet
Connected to openwrt.lan.
Escape character is '^]'.
 === IMPORTANT ============================
  Use 'passwd' to set your login password
  this will disable telnet and enable SSH

BusyBox v1.19.4 (2012-05-10 11:17:53 PDT) built-in shell (ash)
Enter 'help' for a list of built-in commands.

  _______                     ________        __
 |       |.-----.-----.-----.|  |  |  |.----.|  |_
 |   -   ||  _  |  -__|     ||  |  |  ||   _||   _|
 |_______||   __|_____|__|__||________||__|  |____|
          |__| W I R E L E S S   F R E E D O M
 ATTITUDE ADJUSTMENT (Bleeding Edge, r31673)
  * 1/4 oz Vodka      Pour all ingredients into mixing
  * 1/4 oz Gin        tin with ice, strain into glass.
  * 1/4 oz Amaretto
  * 1/4 oz Triple sec
  * 1/4 oz Peach schnapps
  * 1/4 oz Sour mix
  * 1 splash Cranberry juice
Now that the 750GL has booted to ramdisk, the last step is flashing OpenWRT to make it permanent.

WARNING: the next steps will erase the existing RouterOS installation. Make sure to back up the OS, configuration and license first.
root@OpenWrt:/# wget2nand
Connecting to (
kernel               100% |*******************************|  2717k  0:00:00 ETA
Connecting to (
rootfs.tgz           100% |*******************************|  1222k  0:00:00 ETA
Erasing filesystem...
Mounting /dev/mtdblock2 as new root and /dev/mtdblock1 as kernel partition
Copying kernel...
Preparing filesystem...
Cleaning up...
Image written, you can now reboot.  Remember to change the boot source to Boot from Nand
The 750GL should boot OpenWRT natively and respond to pings shortly.