OpenWRT and Linksys WRT54 upgrade tricks

Keeping your managed router up to date is essential for stability and security of it. Modern routers often feature Linux or FreeBSD installations which can be made to your powerful enemies unless taken under control.

I've got in my hands a rather old Linksys WRT54GS v1.1 wireless router with some outdated OpenWRT installed on it. Here I'll show what I have learned about OpenWRT and flashing tricks while updating this router to the newer OpenWRT version.

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Linksys WRT54GS v1.1

This is what I got in my hands:

Linksys WRT54GS v1.1

This article, however, will contain a lot of information, which might also be relevant to other WRT routers, and generally OpenWRT devices. It has sections in it covering different tricks I had to go through while upgrading this router to a newer OpenWRT with LuCi UI.

Serial console and failsafe mode

I can't stress enough, how useful it was to have a serial console connection in the update process. Often the instructions on booting into Failsafe mode just simply did not work reliably.

How to connect Linksys Router to Serial Console?

OpenWRT works perfectly with the serial console and lets you boot into failsafe mode without problems.

For the serial console access I had an 8 Euro adapter with cables. Look for PL2303 USB RS232 in the shop.

This is how it is connected to the router.

USB PL2303 RS232

Pay attention to the yellow VCC cable - it is not connected to the converter. The converter gets its current from the laptop!

The USB-end goes into my Linux laptop, where minicom is installed:

sudo apt-get install minicom

Connect the USB-end now and find a new tty device connected.:

dmesg  |  grep tty 
..
[10016.788473] usb 1-1: pl2303 converter now attached to ttyUSB0
..

Notice the ttyUSB0 device name and start minicom with -s option.

sudo minicom -s

How to make minicom work with OpenWRT and Linksys router?

In the serial port setup specify the device name and switch off the hardware flow control:

A - Serial Device  :  /dev/ttyUSB0
F - Hardware Flow Control : No

Then select Save setup as dfl proceeding to Exit to enter the console. Now you can boot the router.

The failsafe mode in OpenWRT is turned on when you select 'f' and press Enter once the prompt appears for it.

..
Press the [f] key and hit [enter] to enter failsafe mode
Press the [1], [2], [3] or [4] key and hit [enter] to select the debug level
     -- Press f and Enter here.

Reseting OpenWRT to Factory Defaults

Now from the failsafe you can go for factory defaults with.

mount_root; firstboot; reboot

How to reset OpenWRT password?

From there you can also do mount_root; passwd root - to set a new root password, which might be useful if you have a UI access to the old router but do not know its password anymore.

In my case I had a version of OpenWRT without the LuCi GUI. I had to update from the console.

But before that, we need to setup our Linux machine to network with the router.

Network configuration on the Linux Laptop

In my case, it is an Ubuntu laptop. It is done in a similar fashion with other distributions.

How to connect Ubuntu to OpenWRT?

We need to set up a static IP address on your Ethernet NIC and configure the routing. I also put down my other NICs and virtual NICs for the sake of simplicity.

sudo service network-manager stop
sudo ifconfig virbr0 down
sudo ifconfig virbr1 down # cu VirtManager
...
sudo ifconfig docker0 down # ciao docker
sudo ifconfig wlp3s0 down # my WiFi adapter

Check it with ifconfig to find your Ethernet NIC name:

ifconfig
   enp0s31f6 Link encap:Ethernet  HWaddr c8:5b:7...

it is enp0s31f6 in my case.

Connect a patch cable to the port 1 of the router and to your NIC on the laptop.

Let's set some variables and commands:

dev=enp0s31f6
selfaddr=192.168.1.2
selfnm=24
selffulladdr="$selfaddr/$selfnm"
devaddr=192.168.1.1
net=192.168.1.0
netmask=255.255.255.0

alias ro='route -nv'
alias u='sudo ifconfig $dev up'
alias d='sudo ifconfig $dev down'
alias ic='ifconfig $dev'
alias ar='sudo ip route add $devaddr/32 dev $dev'
alias aa='sudo ip addr add $selffulladdr dev $dev'
alias pd='ping -c 3 $devaddr'
alias tn='telnet $devaddr'
alias reconf='d; u; aa; ar; ic; ro; pd'
alias ff='firefox http://$devaddr:80/'

Now let's use them:

d       # puts interface down
u       # brings it up without IP configuration
aa      # adds a static IP to it
ar      # adds the route to the router on the NIC
ic; ro; # verify the configuration
pd      # shall ping the device, if it does not, you have a problem
tn      # telnet to the router
ff      # access Web UI

Now you shall be able to telnet to the router, let's get a new firmware image to install on the router.

How to upgrade OpenWRT from console or telnet?

Getting and converting a firmware image

I got mine from here: https://archive.openwrt.org/chaos_calmer/15.05/brcm47xx/legacy/

It is this one in the bin format.

Basically make sure you check you Exact router version and hardware version of it on the label on the bottom of the router. Then google for OpenWRT wrt54gs v1.1 using your versions of course. And you'll land on a page like this with the right links to the new image: https://wiki.openwrt.org/toh/hwdata/linksys/linksys_wrt54gs

Sysupgrade utility can upgrade the OpenWRT from the console.

Before that we need to convert the image to the trx format expected by older sysupgrade versions. They do not work with bin images producing an error: trx header not found. Do not proceed flashing the bin image, convert it first.

OpenWRT - convert bin to trx image

This is how you do it skipping the first 32 bytes:

dd if=openwrt-15.05-brcm47xx-legacy-linksys-wrt54gs-squashfs.bin bs=32 skip=1 of=openwrt-15.05-brcm47xx-legacy-linksys-wrt54gs-squashfs.trx Check that the new image starts with HDR0:

hd openwrt-15.05-brcm47xx-legacy-linksys-wrt54gs-squashfs.trx | head -n 1
00000000  48 44 52 30 00 10 3a 00  ca 07 46 af 00 00 01 00    | HDR0..:...F.....|

Compare the size difference between the bin and trx files to double check with ls -l and checking the sizes in bytes.

How to upload an image to OpenWRT router?

Prepare the upload on the laptop with nc:

netcat -nlvp 1234 < openwrt-15.05-brcm47xx-legacy-linksys-wrt54gs-squashfs.trx

Then on the router go and download it to /tmp, again with the reduced nc variant in the router's busy box:

cd /tmp
nc 192.168.1.2 1234 > openwrt-15.05-brcm47xx-legacy-linksys-wrt54gs-squashfs.trx

Once the transfer is done, please, perform md5sum on both boxes and compare the checksums for the trx files. They must match on the laptop and on the router.

Updating OpenWRT from sysupgrade

Everything is ready for an upgrade now.

After the download run:

sysupgrade -v openwrt-15.05-brcm47xx-legacy-linksys-wrt54gs-squashfs.trx

And after a while, your router will reboot to the new OpenWRT installation. Don't forget to set a secure password in the LuCi after it.

You can use ff now to connect to it. First, keep the password empty, then set your desired password in the UI by clicking the "Go to password configuration" link, typing a new secure password twice and clicking Save and Apply after that (and not Enter!).

LuCI OpenWRT WebUI

That is it. I hope this article could save you some hassle.

Oh, to bring your normal networking up and running again call sudo service network-manager start.

Thanks for reading my blog!