Thursday, March 19, 2015

The "Funny, It Doesn't Look Like a Linux Server", Server

Check out the cutest edition to our Linux family:

What you're looking at is a TP-Link TL-WA850RE WiFi range extender. A while back, I was having WiFi woes, so I picked up this $30 WiFi extender from Amazon. Turns out, the extender didn't help matters much, so I decided to put it to use in another way.

I installed OpenWRT on the device. OpenWRT is a Linux distribution designed for routers and the like, and it caught my eye because it had confirmed support for this particular device. Installing OpenWRT was almost too easy. I grabbed the .bin file (it was in the ar71xx » generic subdirectory) and used the upload firmware option that was available in the built in web based UI.

In just a few minutes I turned this hunk of white plastic into a Linux box, which, well did nothing. Through some small miracle, I was able to hook it up to a cable and telnet to it.

The first order of business was to configure this device as a WiFi client (or station) rather than the default configuration of being an access point. My hope that was once the device was in client mode, I could plug it into the wall in a random spot in our house, it would then boot up and I'd be able to telnet/ssh to it.

I found this and this article handy is setting up client mode on the device. However, it was ultimately this bit of advice that made all the difference:

If the target network uses the 192.168.1.0/24 subnet, you must change the default LAN IP address to a different subnet, e.g. 192.168.2.1 . You can determine the assigned WAN address with the following command: ...

I had wanted to setup the lan (wired side) of the device to have a static IP and the wan (WiFi side) to have a DHCP picked up IP. It wasn't obvious, but attempting to have both the static IP and dynamic IP be on the same network caused it to fail. The static IP would be set, but the WiFi side wouldn't ever be properly configured. Here's the configuration that ended up working for me:

# /etc/config/wireless
config wifi-device 'radio0'
        option type 'mac80211'
        option channel 'auto'
        option hwmode '11g'
        option path 'platform/ar934x_wmac'
        option htmode 'HT20'
        option disable '0'

config wifi-iface
        option device 'radio0'
        option network 'wan'
        option mode 'sta'
        option ssid 'SSID_TO_CONNECT_TO_GOES_HERE'  # [1]
        option encryption 'wep'
        option key 'PASSWORD_GOES_HERE_SEE_BELOW'   # [2]


# /etc/config/network
config interface 'loopback'
        option ifname 'lo'
        option proto 'static'
        option ipaddr '127.0.0.1'
        option netmask '255.0.0.0'

config interface 'lan'
        option ifname 'eth0'
        option force_link '1'
        option proto 'static'
        option ipaddr '192.168.2.75'     # [3]
        option netmask '255.255.255.0'

# /etc/config/firewall

# ... trimmed ...
config zone
        option name             wan
        list   network          'wan'
        list   network          'wan6'
        option input            ACCEPT  # [4]
        option output           ACCEPT
        option forward          REJECT
# ... trimmed ...

Some notes from above:

[1] - This is where you specify your router's SSID to connect up with
[2] - For WEP encryption I entered a hex value here, versus text. I used this site to do the conversion.
[3] - This was key: my router will give a 192.168.1.x IP, so this needs to be off that network.
[4] - Once I got everything set up, I was getting a connection refused message when trying to telnet to the server. The wan firewall needed to be changed to allow access

Once this all got hashed out, I was able plug the device into a random spot on the wall and telnet to it. Success! And yet, where do I go from here?

Obviously this is useful for educational purposes. I've already had to brush up on my basic networking skills to get this far, and there's plenty more to learn. Heck, you could use this $30.00 router to learn about life on the command line and generally how to be a Unix geek.

OpenWRT, however, is more than just a learning platform. There's a large number of software packages available, and they can be installed using opkg with ease. Turning this bad boy into a web server or the like should be easy enough. I was even able to install a version of scheme, by grabbing an older sigscheme package:

root@pipsqueak:/# opkg install http://downloads.openwrt.org/attitude_adjustment/12.09/ar71xx/generic/packages/sigscheme_0.8.3-2_ar71xx.ipk
Downloading http://downloads.openwrt.org/attitude_adjustment/12.09/ar71xx/generic/packages/sigscheme_0.8.3-2_ar71xx.ipk.
Installing sigscheme (0.8.3-2) to root...
Configuring sigscheme.
root@pipsqueak:/# sscm 
sscm> (map (lambda (x) (* x 9)) '( 1 2 3 4 5 6))
(9 18 27 36 45 54)
sscm> (exit)

Ultimately, what will make this useful is if I can find an application for the device that leverages its near invisible profile and dirt cheap price. If I was in the security business, or a nerd-action-novel writer, then the uses would be pretty obvious. Walk in, plug in device, walk out. And bam! you've got a server that can try to worm it's way onto the network. But for myself, I'm going to have to think a little more on this. Perhaps the device should live in my car? Or maybe it'll be useful in a hotel room? Not sure, but the technology is just too cool to ignore.

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