In some situations, attackers can even sniff data and obtain passwords and other sensitive information. The attack works by taking wrongful advantage of an incorrectly configured trunk port. As you learnt, trunk ports pass traffic from all VLANs (1 – 4094) across the same physical link, generally between switches. The data frames moving across these trunk links are encapsulated with IEEE 802.1Q or ISL to identify which VLAN a frame belongs to.