VLAN hopping is a security vulnerability in networking where an attacker exploits the trunking features of switches to gain unauthorized access to different VLANs (Virtual Local Area Networks). In a VLAN hopping attack, the attacker typically sends frames with manipulated VLAN tags to trick the switch into misinterpreting the traffic. This can allow the attacker to gain access to VLANs other than the one to which they are legitimately assigned. VLAN hopping attacks often target switches configured in dynamic trunking mode, where the switch automatically negotiates trunking with connected devices. To mitigate VLAN hopping, best practices include disabling unnecessary trunking, configuring switch ports as access ports when trunking is not required, and implementing VLAN pruning to restrict VLAN traffic. Additionally, employing network monitoring and intrusion detection systems helps detect and respond to any suspicious VLAN activity.