Wiretap your network

Networking, Security comments edit

When I saw this gadget, I knew I had to have it. Didn’t exactly know what to use it for but it looked and sounded cool. So I ordered one along with a pro version. Unfortunately only the pro version arrived as the other one was out of stock. It would be more fun to build it myself but just seeing it in action is fun too. Of course it’s not as cool as a throwing star but functionality is exactly the same.

LAN Tap Throwing Star

The idea is instead of directly connecting your computer to a switch, you connect the machine to this gizmo and connect the port across to the switch. So essentially getting between the target machine and its final destination for network traffic. The other 2 ports are for monitoring. One of them is for received packets and the other is for the transmitted. Connect a monitoring device to one of these ports and it’s done. The rest is firing WireShark in the monitoring machine and watching the traffic of the other machine. A few cool things about it:

  • It doesn’t require any power source
  • It’s unobtrusive and undetectable

If you want to learn more, here is a nice video about it from Hak5:

Hak5–Throwing Star LAN Tap

I learned that it is commonly used for Intrusion Detection Systems (IDS) so it would be nice to one handy if I can start using one finally. The limitation is of course it only can be used to monitor one target device only. To listen to whole network I’ll need a switch with port mirroring or SPAN support. But for now let’s make sure this device is working properly first. The problem with the pro version is that it doesn’t have any indicators of which ports are for monitoring. So I randomly selected one, connected it between my desktop and the router, connected the laptop to one of the remaining ports. To test it I’m simply pinging google.com. With this confiugration I got nothing, Let’s change the ports and give in another try.. and voila! I filter the packets by my desktop’s IP and ICMP protocol so it’s easy to observe the sniffed packets.


But as you can in the above screenshot there’s a problem: This is only one-way traffic. Let’s use the other monitoring port to see what’s going to change. Another ping to Google and this is what we get:


Now we receive only ping reply packets.As Darren Kitchen mentioned in the Hak5 video we can overcome this problem by using a USB Ethernet adapter with multiple ports. I don’t have one of those so I’ll just take his word for it. Verdict: Only monitoring one machine in one direction makes it a bit useless for me. I was planning to use something to see everything in both directions but overall it was a valuable  experience. After all, before I heard about LAN tapping in a TWIET episode (http://twit.tv/twiet) I didn’t even know such thing existed. Hearing about it in a podcast is nice but nothing beats hands-on experience.