3Com Switch 4200G Configuration Guide

72 CHAPTER 14: BASIC PORT CONFIGURATION
Setting Loopback
Detection for an
Ethernet Port
Loopback detection is used to monitor if loopback occurs on a switch port.
After you enable loopback detection on Ethernet ports, the switch can monitor if
external loopback occurs on them. If there is a loopback port found, the switch will
put it under control.
■ If loopback is found on an access port, the system disables the port, sends a Trap
message to the client and removes the corresponding MAC forwarding entry.
■ If loopback is found on a trunk or hybrid port, the system sends a Trap message to
the client. When the loopback port control function is enabled on these ports, the
system disables the port, sends a Trap message to the client and removes the
corresponding MAC forwarding entry.
CAUTION:
 To enable loopback detection on a specific port, you must use the
loopback-detection enable command in both system view and the specific port
view.
 After you use the undo loopback-detection enable command in system view,
loopback detection will be disabled on all ports.
 The commands of loopback detection feature cannot be configured with the
commands of port link aggregation at the same time.
Configuring the
Ethernet Port to Run
Loopback Test
You can configure the Ethernet port to run loopback test to check if it operates
normally. The port running loopback test cannot forward data packets normally. The
loopback test terminates automatically after a specific period.
Table 54 Set loopback detection for an Ethernet port
Operation Command Remarks
Enter system view system-view —
Enable loopback detection
globally
loopback-detection enable Optional
By default, loopback detection is
disabled globally.
Set time interval for port
loopback detection
loopback-detection
interval-time time
Optional
The default interval is 30 seconds.
Enter Ethernet port view interface interface-type
interface-number
—
Enable loopback detection
on a specified port
loopback-detection enable Optional
By default, port loopback
detection is disabled.
Enable loopback port
control on the trunk or
hybrid port
loopback-detection control
enable
Optional
By default, loopback port control
is not enabled.
Configure the system to
run loopback detection on
all VLANs for the trunk and
hybrid ports
loopback-detection per-vlan
enable
Optional
By default, the system runs
loopback detection only on the
default VLAN for the trunk and
hybrid ports.
Display port loopback
detection information
display loopback-detection Optional
You can use the command in any
view.
Table 55 Configure the Ethernet port to run loopback test
Operation Command Remarks
Enter system view system-view —
Enter Ethernet port view interface interface-type interface-number —