Creating a Bluetooth Access point (NAP) in Ubuntu 11.10

A Bluetooth NAP is similar to a Wi-Fi access point. In this case, we will be using NAP to share an Internet connection to another computer with Bluetooth. It is supposed to be able to support 7 or 8 devices connected at once in this manner. Eventually my personal goal is to use this in conjunction with a Wi-Fi connection to get slightly more speed at once or for some redundancy to help achieve a more ubiquitous/pervasive connection.

It turns out what should be a simple process is a bit tricky in Ubuntu. You would expect to be able to create an IP access point fairly easily so that you can share your Internet connection to other devices using Bluetooth. (It turns out it may be possible with Blueman – http://blog.larsstrand.org/2009/04/sharing-internet-connection-over.html, but I’ve never had any luck with setting it up this way.) Here’s some of the steps and resources I used to get it to work. I am using one laptop with a generic usb dongle and another toshiba netbook with built-in Bluetooth for this.

Before anything is started, you need to make sure the devices are paired and trusted with one another. I found the easiest way to get this to work is with blueman (it is in the Ubuntu repos). Also it seems to work better if you initiate the pairing from the client (the computer not sharing the connection).

First, you need a bridge interface. This is easy enough in Ubuntu, by editing the /etc/network/interfaces file. If the interface you wish to share is eth0 (if you want to share a Wi-Fi connection instead, you could switch this with something like wlan0 or whatever your Wi-Fi interface is), you could add something like this:

auto br1
iface br1 inet dhcp
	bridge_ports eth0
	bridge_fd 9
	bridge_hello 2
	bridge_maxage 12
	bridge_stp off

Next you need to make sure both computers can see each other via Bluetooth. This requires enabling scanning and turning the NAP into a master and the client(s) into slaves. This can be done as follows:

sudo hciconfig hci0 piscan

and

sudo hciconfig hci0 lm MASTER,ACCEPT

or

sudo hciconfig hci0 lm SLAVE,ACCEPT

You can now check to see if each of the computers can see each other on bluetooth by running:

hcitool scan

where you should be able to see the opposite computer on each.

Next you want to start the NAP server on the computer you wish to share the connection from. (This is the computer with the bridge device). This script, which is available on the git repository will allow you to start up the NAP server. (it may also be possible to use pand, but I haven’t had any luck yet with it)
This script is called test-nap. It takes a single argument, which is the name of the bridge device. So in our case we would first need to chmod +x the file (to make it executable), then run it like this:

./test-nap br1
#!/usr/bin/python

import sys
import time
import dbus
from optparse import OptionParser, make_option

bus = dbus.SystemBus()

manager = dbus.Interface(bus.get_object("org.bluez", "/"),
"org.bluez.Manager")

option_list = [
make_option("-i", "--device", action="store",
type="string", dest="dev_id"),
]
parser = OptionParser(option_list=option_list)

(options, args) = parser.parse_args()

if options.dev_id:
adapter_path = manager.FindAdapter(options.dev_id)
else:
adapter_path = manager.DefaultAdapter()

server = dbus.Interface(bus.get_object("org.bluez", adapter_path),
"org.bluez.NetworkServer")

service = "nap"

if (len(args) < 1): bridge = "tether" else: bridge = args[0] server.Register(service, bridge) print "Server for %s registered for %s" % (service, bridge) print "Press CTRL-C to disconnect" try: time.sleep(1000) print "Terminating connection" except: pass server.Unregister(service)

After this, you can search from the client to see if the NAP service can be discovered with the command:

sdptool search NAP

You should be able to see the NAP service from your server machine at this point.

The last thing to do is edit the /etc/network/interfaces file on the client side (the device which will connect to the Internet via Bluetooth. When pand connects, it uses a bnep0 interface. You need to add the following to your file:

iface bnep0 inet dhcp

Now we are ready to connect. This is how you connect:

pand -c 
sudo ifup bnep0

Links:

Aircrack suite + Ubuntu 11.10 problems with monitor mode channel

Recently I have been playing around with the aircrack suite and in particular the aireplay-ng tool. This tool may be used for ARP replay attacks, however it requires that the monitor mode interface is able to switch channels to the channel of the target device / access point. For some reason my monitor interface was stuck in channel -1. So to fix this I found a forum post on Ubuntu Forums which solves this problem: http://ubuntuforums.org/showpost.php?p=10550806&postcount=6

You can apply this to the wlan interface to put it directly into monitor mode and avoid using the airmon-ng tool altogether if you wish. You may also be able to apply this to the mon0 interface created by the airmon-ng tool as well, however I have not tried it yet.

The bulk of the problem is just the order in which monitor mode and channel are enabled, it must follow the order as follows:
ifconfig $IFACE down
iwconfig $IFACE mode managed
ifconfig $IFACE up
iwconfig $IFACE channel $@
ifconfig $IFACE down
iwconfig $IFACE mode monitor
ifconfig $IFACE up

Hope this solves some problems…