HP A5120 EI Series Configuration Guide

12
To do…
Use the command…
Remarks
Enter
Ethernet
interface
view or port
group view
Enter Ethernet
interface view
interface interface-type interface-
number
Use either command.
To configure loopback detection
on one interface, enter Ethernet
interface view.
To configure loopback detection
on a group of Ethernet interfaces,
enter port group view.
Enter port group
view
port-group manual port-group-
name
Enable loopback detection on the
interface
loopback-detection enable
Required
Disabled by default.
Enable loopback detection control
loopback-detection control enable
Optional
Disabled by default.
Enable loopback detection in all
VLANs on the trunk or hybrid
interface
loopback-detection per-vlan
enable
Optional
By default, a trunk or hybrid
interface performs loopback
detection only in its PVID.
Set the protective action to take
on the interface when a loop is
detected
loopback-detection action {
shutdown | semi-block | no-
learning }
Optional
By default, a looped interface
discards all incoming packets but
still forwards outgoing packets.
The system generates traps and
deletes all MAC address entries
of the looped interface.
With the shutdown keyword used,
the switch shuts down looped
Ethernet interfaces and sets their
physical state to Loop down.
When a looped interface
recovers, you must use the undo
shutdown command to restore its
forwarding capability.
NOTE:
 To use single-port loopback detection on an Ethernet interface, you must enable the function both globally and
on the interface.
 To disable loopback detection on all interfaces, run the undo loopback-detection enable command in system
view.
 To enable a hybrid or trunk interface to take the administratively specified protective action, you must use the
loopback-detection control enable command on the interface.
 When you change the link type of an Ethernet interface by using the port link-type command, the switch
removes the protective action configured on the interface. For more information about the port link-type
command, see the Layer 2—LAN Switching Command Reference .
Enabling multi-port loopback detection
When an interface receives packets sent from another interface on the same switch, a loop occurs
between the two interfaces. Such a loop is called a "multi-port loop". As shown in Figure 5, if Port 1
receives packets sent out Port 2, a multi-port loop occurs between the two interfaces, and Port 1 (the

HP A5120 EI Series Specifications

General

Uplink Ports	4 x SFP
Stacking	No
Management	CLI, Web, SNMP
Routing Protocols	RIP, OSPF
Power Supply	AC
MAC Address Table Size	16K
Dimensions	440 x 430 x 44 mm
Operating Temperature	0°C to 45°C
Operating Humidity	10% to 90% non-condensing
Model	HP A5120-24G EI Switch (JG234A)
VLANs	4094