The instructions provided in the following sections are geared towards the user running BeagleBridge on a home network. The bridge will consume some otherwise unused bandwidth and donate it to the Tor network. You should check your ISP's Terms of Service before running a server to see whether it's permitted. Also, you'll need to configure port forwarding from your home router. As there are numerous devices, each with their own configuration mechanism, you should consult your router's manual on how to enable port forwarding.

A bridge, by definition, is the entry point to the Tor network. As such, the exit policy, which will allow traffic to exit the Tor network from the server, should be the following:

ExitPolicy reject *:*

This prevents your server from running as an exit node. If you do decide to run an exit node, be prepared to receive some complaints from your ISP if you are running it on a home network. This is why the Tor Project and the Electronic Frontier Foundation recommend that you don't run an exit relay on a home network. A thorough, legal FAQ prepared by the Electronic Frontier Foundation can be found at https://www.torproject.org/eff/tor-legal-faq.html.en.

There are three bridge specific settings: BridgeRelay, ServerTransportPlugin, and ExtORPort. The BridgeRelay setting is the key setting that defines your relay as a bridge. Your bridge's meta information is published in the bridge database instead of the public directory server, which keeps your bridge's IP less public than a Tor relay's IP address. ServerTransportPlugin defines which pluggable transport proxy your bridge supports. Currently, ScrambleSuit is the latest promising pluggable transport technology. However, obfs3, which is the transport enabled in our bridge configuration example, is slightly more mature and it is the more conservative recommendation. Lastly, ExtORPort allows the gathering and reporting of bridge statistics to the Tor Project.

With the time updated and the configuration set, it's time to turn on the bridge. At the moment, the bridge should be able to make a connection to the Tor network, but it will not be able to accept incoming connections as we have not yet configured port forwarding from your router. However, the obfsproxy port is randomly assigned, so we need to run the bridge first to find the port. Restart the Tor service with the following command:

sudo service tor restart

Next, let's check the log to see whether Tor has started correctly:

tail -n 20 /var/log/tor/notices.log

If you see something like the following, then your Tor client's behavior is working:

Mar 25 21:37:43.000 [notice] Tor has successfully opened a circuit. Looks like client functionality is working.
Mar 25 21:37:43.000 [notice] Bootstrapped 100%: Done.

We know that we need to forward port 9001, as it is the ORPort, but we need to know which port the obfsproxy software runs on. This will be logged in the same file and will be discovered by searching the Tor log with the following command:

grep obfs3 /var/log/tor/notices.log

The previous command should yield the following search result:

Mar 05 01:56:04.000 [notice] Registered server transport 'obfs3' at '0.0.0.0:59519'

The obfsproxy port for our obfs3 service is on 59519. From your home router, configure port forwarding from 9001, and configure port forwarding from 59519 from your external IP to BBB. It will also help if you give your BBB a static internal IP. Consult your router's manual for directions. Alternatively, you can specify the port with the following line in the /etc/tor/torrc file:

ServerTransportListenAddr obfs3 0.0.0.0:xxxx

Replace the x's with the desired port address. However, it's best to let obfsproxy pick a random...

Now you have a Tor bridge running and you can stop here. If you do, you'd be missing out on the ability to combine software with custom hardware on BBB. Our BBB Tor bridge currently has no visual feedback, so it's not obvious that it's working. Also, the only means to control the bridge is to log in to BBB over SSH and manipulate the configuration options. The Tor bridge is an appliance and it needs appliance controls. In this section, we'll add a front panel, which will give us an easy method to control the bridge's bandwidth and a quick indicator to know that the software hasn't crashed. In the following section, we'll add the software to interface with our bridge and control the hardware.