Shag simulates an additional ethernet device over an existing one. It is useful for testing the security of your switch, or if your machine is on a private VLAN and you want to see another VLAN without another ethernet card.
You can download it from the following link: https://packetstormsecurity.com/files/download/16872/Shag.tar.gz
Source: https://packetstormsecurity.com/files/16872/Shag.tar.gz.html