Enabling Loopback Detection On An Ethernet Interface - 3Com 4210G Series Configuration Manual

To do...
Enable the
forwarding of
jumbo
frames

Enabling Loopback Detection on an Ethernet Interface

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 an interface.
When loopback detection is enabled on an Ethernet interface, 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 interface 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
port-group manual
In port-group
port-group-name
view
jumboframe enable
interface interface-type
In Ethernet
interface-number
interface view
jumboframe enable
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
Use the command...
Use the command...
1-8
Remarks
Use any command.
By default, the device
allows jumbo frames with
the length of 9,216 bytes
to pass through all Layer 2
Ethernet interfaces.
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