Creating a Tor Relay

If you want to get deeper into using Tor, try becoming a relay. If you configure a relay system, you are contributing to the Tor network. Relaying servers communicate with the rest of the Tor network by default on TCP Port 9001.

To configure Tor to relay remote connections, edit the /etc/tor/torrc file and change the SocksPort value to read:

SocksPort 0

As a result, this system will not accept local connections. Of course, you can change the standard SocksPort value to anything you wish, but I prefer using the above value. Once you have made the above changes, restart Tor so that they take effect. Now, your system will become part of the Tor network. For more configuration options, see the box titled "Throttling and Listening Addresses."

RelayBandwidthRate 50 KB     # Throttle traffic to 50KB/s (400Kbps)

RelayBandwidthBurst 100 KB    # But allow bursts up to 100KB/s (800Kbps)

AccountingMax 1 GB

## Each period starts daily at midnight    (AccountingMax is per day)
AccountingStart month 9 11:00

SocksListenAddress 192.168.15.3:9050

Creating a Rendezvous Point

It is possible to mask your instance of your Tor system. A masked server is called a rendezvous point. In this case, Tor no longer listens on default ports. You can specify a port, which helps mask the instance. You can also make your system appear as if it is simply running a web server, when it is actually running Tor.

For example, you can advertise your Tor server as an SSL/TLS-protected web server that listens on the standard TCP port 443. Yet your system is actually simply forwarding connections on port 443 to Tor, which is listening on custom port number 9191:

ORListenAddress 0.0.0.0:9191

The preceding entry tells Tor to listen on the 9191 port. You will, however, need to forward your IP traffic from port 443 to the proper port using iptables:

iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 443 -j REDIRECT --to-ports 127.0.0.1:9191

The preceding entry tells your system to forward connections going to port 443 to the port you have specified. Remember that each time you edit the /etc/tor/torrc file, you will need to restart Tor.

Timing is Everything with Tor

As with most network-aware services, it's important to make sure your system has accurate clock settings. Your computer will have to work and play well with other systems, which means you'll need to be sure you have accurate information for the date, time zone, and clock time.

If your system doesn't have coherent time settings, your traffic will get dropped. System time is especially critical when configuring tor as a relay.

So, make sure you install and run a good Network Time Protocol (NTP) client, such as Open NTP (openntpd). You don't need to become an NTP server. Most Linux distros have these services already installed and running; however, if you don't have them, take the necessary steps. In my Ubuntu Linux system, I would issue the following command to get the client:

$ sudo apt-get install ntpdate

The following command installs the server, in case you should need it:

$ sudo apt-get install openntpd

Your commands will differ if you're using a Red Hat-based system, of course. Once you have installed the relevant NTP element, make sure you have edited the relevant files, which might include /etc/ntp.conf. Then, add at least two time server entries, such as:

server im.pool.ntp.org, server pool.ntp.org

You might need to edit your network perimeter firewall settings as well. Your network perimeter firewall will be the most likely culprit for blocking NTP-based traffic. However, I've also run into instances where zealous individuals use iptables to manage and block traffic types. So, make sure you have unblocked NTP-based ports on your local system in addition to your perimeter firewall.