Overview of Loopback Detection

Loopback detection sends loopback detection packets periodically to detect loops on the network connected to the device. When a loop occurs on a network, broadcast, multicast, and unknown unicast packets are repeatedly transmitted on the network. This wastes network resources or even causes service interruption on the entire network. To protect the network, certain actions should be taken on the interface where the loop occurs, and the administrator needs to check the network connection and configuration to solve the problem soon. Therefore, a mechanism is required on a Layer 2 network to detect loops and notify the administrator.

Loopback detection is such a mechanism. It sends detection packets from an interface at intervals and checks whether the packets are sent back to the interface. If the packets are sent back, a loopback occurs on the interface.