Enabling MAC Flapping-based Loop Detection

Procedure

1. Run system-view

   The system view is displayed.

2. Run vlan vlan-id

   The VLAN view is displayed.

3. Run loop-detect eth-loop loop-times loop-times detect-cycle detect-cycle-time cycles cycles { alarm-only | retry-times retry-times block-time block-time }

   MAC flapping-based loop detection is enabled, and its parameters are configured.

   retry-times retry-times and block-time block-time must both be specified. For example, retry-times is specified as 2 and block-time as 100s. When detecting loops in the VSI, the device blocks interfaces using the following methods:

   1. When detecting a loop on an interface for the first time, the device keeps the interface blocked for 100s.
   2. During the first detection cycle (specified by detect-cycle-time) after the first blocking period ends (the blocked interface recovers), if the device detects a loop, it keeps the interface blocked for 2 x 100s.
   3. During the second detection cycle (specified by detect-cycle-time) after the second blocking period ends, if the device detects a loop, it keeps the interface blocked for 4 x 100s.
   4. During the third detection cycle (specified by detect-cycle-time) after the third blocking period ends, if the device detects a loop, it keeps the interface blocked permanently. The reason for the permanent blocking is that three loops occur after the first blocking period ends, which exceeds the maximum number of loops specified by retry-times.

   

   If no loops are detected during detect-cycle-time*30, the blocking count is cleared. If a loop is detected later block-time is restored.

   

   On an STP-capable Layer 2 network, packets with the same source MAC address may form loops. To prevent loops, an interface must be blocked, and an alarm must be reported to the NMS. To allow both STP and MAC flapping-based loop detection to be enabled, run the loop-detect eth-loop assist-stp enable command.

   STP and MAC flapping-based loop detection have different blocking principles and may block different interfaces on a network, leading to temporary traffic interruptions. Therefore, exercise caution when running the loop-detect eth-loop assist-stp enable command.

4. Run commit

   The configuration is committed.