L2 network filtering can be bypassed using stacked VLAN0 and LLC/SNAP headers

Network filtering systems that check Layer 2 traffic can be bypassed by crafting packets with stacked VLAN 0 headers combined with LLC/SNAP headers. This allows attackers to send dangerous traffic (like IPv6 router advertisements or ARP spoofing) that security tools fail to detect.

Layer 2 filtering mechanisms (IPv6 RA Guard, ARP inspection) fail to properly validate packets containing nested VLAN 0 tags paired with LLC/SNAP encapsulation, allowing bypass via crafted Layer 2 frames. An attacker on the local network segment can exploit this to inject undetected ARP or IPv6 RA packets, potentially enabling man-in-the-middle or denial-of-service attacks.