Introduction to LBDT and LDT
Loopback detection (LBDT) and loop detection (LDT) periodically send detection packets through an interface to detect loops on the interface, on the downstream network or device, or between two device interfaces.
When a loop occurs on a network, broadcast, multicast, and unknown unicast packets are circulated on the network. This wastes network resources and can result in network breakdowns. Quickly detecting loops on a Layer 2 network is crucial for users to minimize the impact of loops on a network. LBDT and LDT help users check network connections and configurations, and control the looped interface.
LDT and LBDT periodically send detection packets on an interface to check whether the packets return to the local device (through the same interface or another interface), and determines whether a loop occurs on the interface, on the downstream network or device, or between two device interfaces. After a loop is detected, the device sends a trap to the NMS and records a log, and takes a preconfigured action on the looped interface (the interface is shut down by default) to minimize impact of the loop on the device and entire network.
LDT and LBDT can only detect loops on a single node, but cannot eliminate loops in the same manner as ring network technologies including ERPS, RRPP, SEP, Smart Link, STP, RSTP, MSTP, and VBST.
The switch support LDT and LBDT. Table 20-1 describes the differences between LDT and LBDT.
Item |
LDT |
LBDT |
|---|---|---|
Detection packet |
Sends only tagged detection packets, so loops are detected based on VLANs. |
Sends tagged and untagged detection packets, so loops are detected based on interfaces and VLANs. |
Action taken after a loop is detected |
Provide Trap, Block, Shutdown, No Learning, and Quitvlan actions. (See Action Taken After a Loop Is Detected.) |
|
Automatic recovery of the looped interface |
Attempts to restore the interface when detection packets are not received within the recovery time. |
Attempts to restore the interface after the recovery time. However, the interface shut down by LBDT cannot be restored. |
Applicable scenario |
Detect loopbacks on an interface, loops on the downstream network or device and loops between two device interfaces |
|
Deployment |
|
|
Maximum number of VLANs that can be detected |
4094 |
8 |