addresses flap in a short time on the network, MAC address flapping is caused by loops. When
a loop occurs and causes a broadcast storm, MAC address flapping occurs on each switch
affected by the broadcast storm. Therefore, MAC address flapping detection can be used to check
for loops on a network.
MAC Address Flapping Detection
The device can detect MAC address flapping. When MAC address flapping occurs, the device
can provide diagnosis information, including the flapping MAC address, interfaces between
which the MAC address flaps, and VLAN that the interfaces belong to. A loop may exist on the
interfaces between which the MAC address flaps. You will know how the loop is generated by
checking interfaces where MAC addresses are flapping.
Figure 1-2 MAC address flapping detection
SwitchA
Router
SwitchB SwitchC
Broadcast
storm
Network
Users
Port1
Port2
MAC:11-22-33
MAC:11-22-33
Data flow
Incorrect
connection
Access port
As shown in Figure 1-2, Switch B should not be connected to Switch C. When the two switches
are connected, Router, Switch B, and Switch C form a loop. When Port1 of Switch A receives
a broadcast packet, Switch A forwards the packet to Switch B. The packet is then sent to Port2
of Switch A. Switch A detects that the source MAC address of the packet flaps from Port1 to
Port2. If the MAC address flaps between the two ports frequently, Switch A considers that MAC
address flapping occurs.
NOTE
l MAC address flapping detection allows a router to detect changes in traffic based on learned MAC addresses,
but the router cannot obtain the entire network topology. It is recommended that this function be used on an
interface when the interface connects to a user network where loops may occur.
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
1 MAC Address Table Configuration
Issue 01 (2014-11-30) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
6
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