Enabling Multi-Port Loopback Detection - HP 5820X series Configuration Manual

To do...
8. Set the protective action to
take on the interface when a
loop is detected
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
perform the loopback-detection control enable command on the interface.
When you change the link type of an Ethernet interface with 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 out 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
packets sent out Port 2, a multi-port loop occurs between the two interfaces, and Port 1 (the interface that
receives the looped packets) is the looped interface. Multi-port loops may also cause broadcast storms.
Figure 5 Network diagram for multi-port loopback detection
The multi-port loopback detection function detects loops among interfaces on your switch. Use the
loopback-detection action command to configure the protective action to take on looped interfaces, for
example, to shut down the interface, eliminating the loops. In addition, the switch also takes other link
type-dependant actions on the looped interface (for example, Port 1 in
Use the command...
loopback-detection action
{ shutdown | semi-block | no-
learning }
16
Remarks
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.
Figure 5, if Port 1 receives
Figure 5) to alleviate the impact of