Without Spanning Tree Protocol (STP), Layer 2 loops can occur, causing broadcast, multicast, and unknown unicast frames to loop endlessly. This can lead to network failure in seconds. For example, broadcast frames like ARP Requests are forwarded to all switch ports, except the original ingress port. If there are multiple paths, the frames can loop endlessly, destabilizing the MAC address table. This instability can result in high CPU usage, making the switch unable to forward frames. Similarly, unknown unicast frames can cause duplicates to reach their destination if the MAC address is not in the switch's table.