Exploitation Packet Analysis Packet Crafting Voice Over IP
VoIP Hopper is a GPLv3 licensed security tool, written in C, that rapidly runs a VLAN Hop into the Voice VLAN on specific Ethernet switches. VoIP Hopper does this by mimicking the behavior of an IP Phone, in both Cisco and Avaya IP Phone environments. VoIP Hopper is a VLAN Hop test tool but also a tool to test VoIP infrastructure security.
In Cisco IP Phone networks, it first dissects either IEEE 802.3 or Ethernet II for Cisco Discovery Protocol (CDP) packets. If CDP is enabled on the switch port and the Voice VLAN feature is enabled, it will determine the Voice VLAN ID (VVID). This will allow the tool to create a new Ethernet interface on the PC that tags the 802.1q VLAN header in the Ethernet packet. After VoIP Hopper has created the new Ethernet device, it will send a DHCP client request. It can also generate CDP messages just as an IP Phone based on CDP would do. It will send two CDP packets, requesting the Voice VLAN ID. After creating the new interface, it will then iterate between sleeping for 60 seconds, and sending a CDP packet.