VLAN hopping

VLAN Hopping is an attack where the attacker is able to send traffic from one VLAN into another. There are two different methods to accomplish this:

• Double tags: the idea behind the attack is that the attacker is connected to an interface in access mode with the same VLAN as the native untagged VLAN on the trunk. The attacker sends a frame with two 802.1Q tags, the “inner” VLAN tag is the VLAN that we want to reach and the “outer” VLAN tag is the native VLAN. When the switch receives the frame, it will remove the first (native VLAN) 802.1Q tag and forwards the frame with the second 802.1Q tag on its trunk interface(s). The attacker has now “jumped” from the native VLAN to the victim’s VLAN.It’s a one way trip but it could be used perhaps for a DOS attack.
• Switch spoofing: the attacker will send DTP packets and tries to negotiate a trunk with the switch, this is possible when you use the default “dynamic auto” or “dynamic desirable” switchport mode. Once you have a trunk to your computer, you will have access to all VLANs. This is basically a misconfiguration since you should never configure your interfaces to use the dynamic switchport modes.