Is Your Personal Area Network Giving You the BlueZ?

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Bluetooth is a complex beast, and recent changes to the standard Linux implementation have bamboozled many users. Untangle your personal area network with this revealing article on setting up the Bluetooth PAN Profile in BlueZ v.4.
The Route of the Problem

For the routed solution, you need to create a separate network/subnet for your PAN and route packets between this and the existing private network/ISP-connected machine. In this configuration pan0 will be the default gateway device and also provide the DHCP service for the PAN. Thus, pan0 will require a static IP configuration and its DHCP service will be separate from any other DHCP and dedicated to the PAN. For clarity, let's use the 10.0.0.0/24 private IP network range for this purpose. This time, there are four steps to get your routed PAN up and running:

  1. Configure pan0 with static IP information.

  2. Configure and run DHCP for the PAN.

  3. Turn on IP forwarding to route packets between pan0 and wlan0/eth0.

  4. Enable NAT on the wlan0/eth0 interface.

Then:

ifconfig pan0 10.0.0.1 netmask 255.255.255.0 
 ↪broadcast 10.0.0.255 up

Use your system tools to make permanent settings.

Below is a small DHCP configuration for the routed PAN:

# small dhcp config for bluetooth PAN
ddns-update-style none;
authoritative;

subnet 10.0.0.0 netmask 255.255.255.0 {
range 10.0.0.10 10.0.0.100;
option domain-name-servers 192.168.0.1;
option domain-name "bluetooth.net";
option routers 10.0.0.1;
option broadcast-address 10.0.0.255;
default-lease-time 600;
max-lease-time 7200;

host btmobile {
hardware ethernet 78:e7:d1:ab:d5:6f;
fixed-address  10.0.0.5;
}
}

Alter the DNS information as necessary.

pan0 should be configured and up and running before you start the DHCP service. The next step involves enabling IP forwarding so that packets are routed between pan0 and your existing interface (wlan0/eth0).

In older systems, IP forwarding is enabled by echoing a value of “1” into the appropriate system file:

echo 1 > /proc/sys/net/ipv4/ip_forward

In more recent systems, this is achieved by editing /etc/sysctl.conf:

# Controls IP packet forwarding
net.ipv4.ip_forward = 1

The setting also may be available in your distribution's firewall configuration GUI tool. If none of these methods work on your system, consult your distribution's documentation.

Finally, you need to tell the kernel netfilter software to “masquerade” (NAT) PAN packets through the wlan0/eth0 interface. You may be able to do this using your distribution's firewall configuration GUI tool (the IP forwarding setting may be available here too). If not, it can be achieved using the iptables command:

iptables -A POSTROUTING -t nat -o wlan0 -j MASQUERADE

Substitute eth0 for wlan0 if you are using the routing option because your Linux box connects directly to your ISP and your eth0 interface has an ISP-assigned, routable IP address (Figure 2).

Figure 2. Routed NAP Solution

If all has gone well up to this point, your NAP service should be active a few seconds after you connect/authenticate your remote BT device. You should, for example, be able to ping the device from your Linux box. If IP is not yet running, you can use l2ping <MAC-ADDRESS> to ping the remote device.

Oh, for the Simple Life

BlueZ v.4 does not appear to provide separate configurations for GN and PANU modes of PAN operation, but this is of no consequence because, as was noted above, these are subsumed by the NAP mode. If you only want to connect remote BT devices to your Linux box, and do not require access to the local network or Internet, you simply can omit step 1 from the bridged solution and either employ the DHCP configuration from the routed solution or manually set IP parameters for pan0 and your BT devices.

In fact, Bluetooth is supposed to implement the draft Link-local Autoconfiguration Protocol (variously known elsewhere as Avahi, Bonjour, Rendezvouz and APIPA), so you could try using this for IP configuration instead of running a DHCP service. However, I had no joy with this approach under BlueZ v.4, so I leave it as a potential solution for those of an experimental nature. I would be happy to hear that this facility is alive and well in the BlueZ package if anyone succeeds where I have failed.

Nostalgia Is Not What It Used to Be

For those who want to retain the old ways of configuring and running the Bluetooth facilities, the development team has provided a legacy implementation in the form of a package that contains the separate dæmons as provided in BlueZ 3.x. This package is called Bluez-compat and should satisfy the change-resistant among you. Michael Schmidt (see Resources) has produced a useful how-to document covering the legacy formats.

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how to setup pan0

digitalcubano's picture

Hi,

This article is a non-starter for me as the bluetooth daemon fails to create a pan0 device. Any pointers on configuring the myriad config files to get bluetoothd to create pan0?

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