Enabling Loopback Detection On An Ethernet Port; Configuring The Mdi Mode For An Ethernet Port - H3C S5120-EI Series Operation Manual

Enabling Loopback Detection on an Ethernet Port

If a port receives a packet that it sent out, a loop occurs. Loops may cause broadcast storms. The
purpose of loopback detection is to detect loops on a port.
When loopback detection is enabled on an Ethernet port, the device periodically checks whether the
ports have any external loopback. If it detects a loopback on a port, the device will set that port to be
under loopback detection mode.
If loops are detected on an access port, the port will be blocked. Meanwhile, trap messages will be
sent to the terminal, and the corresponding MAC address forwarding entries will be removed.
If loops are detected on a trunk port or a hybrid port, trap messages are sent to the terminal. If the
loopback detection control function is also enabled on the port, the port will be blocked, trap
messages will be sent to the terminal, and the corresponding MAC address forwarding entries will
be removed.
Follow these steps to configure loopback detection:
To do...
Enter system view
Enable global loopback
detection
Configure the interval for port
loopback detection
Enter Ethernet port view
Enable loopback detection on a
port
Enable loopback detection
control on a trunk port or a
hybrid port
Enable loopback detection in all
the VLANs to which trunk or
hybrid ports belong
Loopback detection on a given port is enabled only after the loopback-detection enable
command has been configured in both system view and the port view of the port.
Loopback detection on all ports will be disabled after the configuration of the undo
loopback-detection enable command under system view.

Configuring the MDI Mode for an Ethernet Port

Use the command...
system-view
loopback-detection enable
loopback-detection
interval-time time
interface interface-type
interface-number
loopback-detection enable
loopback-detection control
enable
loopback-detection per-vlan
enable
1-8
Remarks
—
Required
Disabled by default
Optional
30 seconds by default
—
Required
Disabled by default
Optional
Disabled by default
Optional
Enabled only in the default
VLAN(s) with trunk port or
hybrid ports