This article describes how I set up two wireless routers in my apartment, to provide a PSK2 encrypted wireless connection for all my household equipment. They are linked together using WDS (also PSK2). I use OpenWRT built directly from SVN. For hardware, I'm using two Asus WL-500G Premium (which uses a broadcom-based wlan).

Wireless Network Illustration

If you need a 3G connection as well, you may find my summer house wireless+3g network writeup more relevant.

If you want to comment on this, please go to the blog entry.

Created by Simon Josefsson on 2008-05-08.

Building OpenWRT

Building OpenWRT is quite easy these days. I'm using Debian x86 lenny, and you will need to install gcc and other development tools. Here are the commands I used:

svn co https://svn.openwrt.org/openwrt/trunk/
mv trunk openwrt
cd openwrt
make menuconfig
#  toggle 'select all packages by default'
#  quit and save config
make

That's it! The complete build takes up about 2GB on my machine, and it will take quite some time to build (up to several hours).

The output files will be stored into the bin/ directory.

In case you also have the WL-500gP, and trust my build, you can download files from my online build tree. You will probably only need the openwrt-brcm-2.4-squashfs.trx file.

Installing OpenWRT

There are generic Installation instructions on the the OpenWRT Wiki.

You'll have to use a ethernet cable at this point. Connect it to LAN1-LAN4, not WAN. Configure your local machine on the 192.168.1.x network, for example as 192.168.1.42. The router will use 192.168.1.1.

On many routers, including the Asus WL-500g Premium that I use, you flash an image by disconnecting power, press and hold down the reset button, and connect the power again. Wait a few seconds and the PWR led will start to blink. Release the reset button. The device will now have a tftp server running on 192.168.1.1.

tftp 192.168.1.1
tftp> trace
Packet tracing on.
tftp> binary
tftp> put openwrt-brcm-2.4-squashfs.trx
...

Wait a few minutes and restart the box by disconnecting power briefly. Some documentations claim that the device should restart by itself but I have never seen this happen.

Configuring OpenWRT

When the router has restarted, it will have a telnet server running listening on 192.168.1.1.

jas@mocca:~$ telnet 192.168.1.1
Trying 192.168.1.1...
Automatic decryption of input is enabled
Automatic encryption of output is enabled
Will send login name and/or authentication information.
Connected to 192.168.1.1.
Escape character is '^]'.
 === IMPORTANT ============================
  Use 'passwd' to set your login password
  this will disable telnet and enable SSH
 ------------------------------------------


BusyBox v1.8.2 (2008-05-07 15:40:57 CEST) 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
 KAMIKAZE (bleeding edge, r11058) -------------------
  * 10 oz Vodka       Shake well with ice and strain
  * 10 oz Triple sec  mixture into 10 shot glasses.
  * 10 oz lime juice  Salute!
 ---------------------------------------------------
root@OpenWrt:~#

Now you can configure OpenWRT. I'll go through each step I made, but obviously you may deviate from this description.

Set hostname

My first step was to set a hostname on the machine, use vi to edit /etc/config/system to make it read:

config system
        option hostname caramel

If you prefer to cut'n'paste a command line invocation to do this, try:

root@OpenWrt:~# cat /etc/config/system | sed -e 's/OpenWrt/YOURHOSTNAME/' > /etc/config/system

Setting a hostname will help when you have multiple OpenWRT boxes running, as the command prompt will show your hostname instead of OpenWRT (after you have restarted the router).

Set IP address

If you want the device to use another IP address than 192.168.1.1 you can modify /etc/config/network, in the LAN configuration section. A quick command to do this:

root@OpenWrt:~# cat /etc/config/network | sed -e 's/192.168.1.1/192.168.1.15/' > /etc/config/network

Replace telnet with SSH

As you do not want to use insecure telnet, you will need to set up ssh. You can type passwd to set a root password, and this will disable telnet. I dislike passwords, even if used over ssh, so I always set up public-key authentication instead. For reference, there is a dropbear public key authentication howto for OpenWRT wiki page.

The command to make your ssh key authorized to login as root on the router is:

root@OpenWrt:/# echo 'PUBLICKEY'  > /etc/dropbear/authorized_keys

Replace PUBLICKEY with the content of the ~/.ssh/id*.pub file on your own machine.

Disable password based login using:

root@OpenWrt:/# cat /etc/config/dropbear | sed -e "s/'on'/'off'/"  > /etc/config/dropbear

Alternatively, edit /etc/config/dropbear to look like:

config dropbear
        option PasswordAuth 'off'
        option Port         '22'

The final touch is to disable the telnet server. I also disable the httpd server too, since it doesn't seem to serve any purpose.

root@OpenWrt:~# rm /etc/rc.d/S50telnet /etc/rc.d/S50httpd

At this point, you can print the ssh host key fingerprint using:

root@OpenWrt:~# dropbearkey -y -f /etc/dropbear/dropbear_rsa_host_key
Public key portion is:
ssh-rsa AAAA... root@OpenWrt
Fingerprint: md5 ae:...

Telnet should now be disabled, and you should be able to login as root using SSH. Try it from your machine. The SSH fingerprint should match what was printed by dropbearkey earlier.

jas@mocca:~$ ssh -l root 192.168.1.15
The authenticity of host '192.168.1.1 (192.168.1.15)' can't be established.
RSA key fingerprint is ae:...
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.1.15' (RSA) to the list of known hosts.


BusyBox v1.8.2 (2008-05-07 15:40:57 CEST) 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
 KAMIKAZE (bleeding edge, r11058) -------------------
  * 10 oz Vodka       Shake well with ice and strain
  * 10 oz Triple sec  mixture into 10 shot glasses.
  * 10 oz lime juice  Salute!
 ---------------------------------------------------
root@OpenWrt:~#

Setup wireless

Wireless is disabled by default, and you will have to modify “/etc/config/wireless” to configure it.

A simple setup that use (insecure) WEP would be:

config wifi-device  wl0
        option type     broadcom
        option channel  5

config wifi-iface
        option device   wl0
        option network  lan
        option mode     ap
        option ssid     YourNetworkName
        option encryption wep
        option key      DEADBEEF

A better setup that use shared secrets but the more secure PSK2 would be:

config wifi-device  wl0
        option type     broadcom
        option channel  5

config wifi-iface
        option device   wl0
        option network  lan
        option mode     ap
        option ssid     YourNetworkName
        option encryption psk2
        option key      DEADBEEFDEADBEEFDEADBEEFDEADBEEF

Remember, your security is never better than your password.

As you may recall, the point of my exercise was to set up two routers with WDS and PSK2. For discussion, let's say the MAC address of box 1 is 12:34:56:78:89:ab and the MAC address of box 2 is cd:ef:01:23:45:67. You can use ifconfig on each of the routers to find out the MAC address.

On the first box, my /etc/config/wireless file looks like:

# /etc/config/wireless configuration for device 12:34:56:78:89:ab
config wifi-device  wl0
        option type     broadcom
        option channel  5

config wifi-iface
        option device   wl0
        option network  lan
        option mode     ap
        option ssid     YourNetworkName
        option encryption psk2
        option key      UserNetworkPassword

config wifi-iface
        option device   wl0
        option network  lan
        option mode     wds
        option bssid    cd:ef:01:23:45:67
        option encryption psk2
        option ssid     WDSNetworkName
        option key      InternalWDSPassword

Replace YourNetworkName and WDSNetworkName with something more appropriate. You want to use a different ssid for the WDS than for the normal network.

On the second box, the /etc/config/wireless will look the same except that the bssid will contain the MAC address of the other box. Here is the file:

# /etc/config/wireless configuration for device cd:ef:01:23:45:67
config wifi-device  wl0
        option type     broadcom
        option channel  5

config wifi-iface
        option device   wl0
        option network  lan
        option mode     ap
        option ssid     YourNetworkName
        option encryption psk2
        option key      UserNetworkPassword

config wifi-iface
        option device   wl0
        option network  lan
        option mode     wds
        option bssid    12:34:56:78:89:ab
        option encryption psk2
        option ssid     WDSNetworkName
        option key      InternalWDSPassword

Disable DHCP on one router

Both routers will by default run a DHCP server. The DHCP server and/or DHCP clients may be confused by having two, so it is typically better to just have one running. Disable it on one of the boxes.

root@OpenWrt:~# rm /etc/rc.d/S60dnsmasq

Restart router

After you have made your changes, try the new configuration by rebooting both devices.

root@OpenWrt:/etc/config# reboot

After 30 seconds or so, the devices should have connected via WDS and you should be able to ping the IP addresses of router A from router B and vice verse.

The default configuration is to bridge the wireless networks with the LAN ethernet sockets, so you can connect desktop machines etc and they should be able to reach all devices connected to the wireless network or the ethernet sockets on any of the two WDS connected routers.

Bonus

Given that I placed my OpenWRT bin/ directory accessible over the internet, you can use ipkg to download packages from me. Make sure /etc/ipkg.conf reads:

src snapshots http://josefsson.org/openwrt/brcm-2.4/packages/mipsel
dest root /
dest ram /tmp

Then you can install some tools easily:

root@caramel:~# ipkg update
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/Packages
Updated list of available packages in /usr/lib/ipkg/lists/snapshots
Done.
root@caramel:~# ipkg install ez-ipupdate avahi-daemon
Installing ez-ipupdate (3.0.11b8-3) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./ez-ipupdate_3.0.11b8-3_mipsel.ipk
Installing avahi-daemon (0.6.21-1) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./avahi-daemon_0.6.21-1_mipsel.ipk
Installing libavahi (0.6.21-1) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./libavahi_0.6.21-1_mipsel.ipk
Installing libdaemon (0.12-1) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./libdaemon_0.12-1_mipsel.ipk
Installing libpthread (0.9.29-12) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./libpthread_0.9.29-12_mipsel.ipk
Installing libexpat (1.95.8-1) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./libexpat_1.95.8-1_mipsel.ipk
Configuring avahi-daemon
Configuring ez-ipupdate
Configuring libavahi
Configuring libdaemon
Configuring libexpat
Configuring libpthread
Done.
root@caramel:~# ipkg install miniupnpd
Installing miniupnpd (1.0-RC8-1) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./miniupnpd_1.0-RC8-1_mipsel.ipk
Configuring miniupnpd
Done.
root@caramel:~# ipkg install openntpd
Installing openntpd (3.9p1-2) to root...
Downloading http://josefsson.org/openwrt/brcm-2.4/packages/mipsel/./openntpd_3.9p1-2_mipsel.ipk
Configuring openntpd

adding group ntp to /etc/group
adding user ntp to /etc/passwd
Done.
root@caramel:~#

The End

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