Build your own LAN tap

Having a completely undetectable (except physically finding it) device that sniff traffic is of course something everyone should have. I’ve personally never been very fond of hardware (or tinkering with hardware) and I decided to try to change that somewhat. I bought a soldering iron and ordered some stuff (China <3) from ebay after deciding to craft my own LAN tap. It is probably quite obvious that this is my first time soldering. So, here’s how you build your own, more or less.

What you will need:
* a soldering iron
* 4 RJ-45 female sockets (good to have a few more if you mess up)
* an ethernet network cable


First cut up the network cable and extract the wires inside it. Make them roughly 10 cm each (to allow mistakes while soldering and cutting em up, we want em smaller later) and carefully cut up the wires so the inside is exposed. These will be used as the wire to connect the RJ-45 sockets together. Unfortunately I do not have any pictures of this but it will be clear later on how these look.

We now want to solder 4 RJ-45 sockets together. I choose (for clarity) to point the two sockets in the middle in one direction and the outer in the opposit direction. Carefully solder the borders together on the various sides.


Now, here’s the schematic we’re going to use. If you look careful you’ll notice that the sockets I use got 10 pins and not 8. This caused some trouble before I realised this and had to redo most of the LAN tap. I ended up cutting off two pins on each socket and then redo it. Unfortunately I forgot to take pictures off this.


After studying how the wires are supposed to be connected it is time to start the soldering. Also worth noting is that host and tap have been switched, so the host will be in the middle and the tap will be on the outer part of the tap. I recommend connecting the two hosts first (middle sockets).


Before starting with the fifth (two twined together x 2 as seen on the pictures above) wire plug in the tap and make sure connectivity works between two hosts with ping. After that’s done continue with connecting the wires to the two taps.


Once done the result should look something along the lines of this. Depending on how good you are with soldering the results might vary. ;)


Good luck!