How to determine whether loops occur on a Layer 2 network

To determine whether loops occur on a Layer 2 network, two methods are available:
Run the display interface brief | include up command to view traffic on all Up interfaces. If a loop occurs, the values of InUti and OutUti approximate to 100% when you run the command multiple times, which are greater than the service traffic.

Command output upon the first query is as follows:
[HUAWEI] display interface Ethernet brief | include up
InUti/OutUti: input utility/output utility
Interface PHY Auto-Neg Duplex Bandwidth InUti OutUti Trunk
GigabitEthernet0/0/1 up enable full 1000M 0.56% 0.56% -- Command output upon the last query is as follows:
[HUAWEI] display interface Ethernet brief | include up
InUti/OutUti: input utility/output utility
Interface PHY Auto-Neg Duplex Bandwidth InUti OutUti Trunk
GigabitEthernet0/0/1 up enable full 1000M 76% 76% -- Determine whether MAC address flapping occurs on the switch.
Run the display mac-address command. If different interfaces of the switch learn the same MAC address, MAC address flapping occurs.
Configure MAC address flapping detection on the switch. If MAC address flapping is detected, the switch generates an alarm. For details about how to configure MAC address flapping detection, see How Do I Configure MAC Address Flapping Detection?

Scroll to top