Administrator Guide

○ pe-stack-unit-id is a PE stack-unit ID number from 0 to 7.
Dell# reset pe 0 stack-unit 1
Preventing Loops on Port Extender Ports
The existing behavior of Loop detection module is a simple loop detection mechanism in L2 to detect loops between PE
interfaces and break the loop. This mechanism is purely based on the data traffic sent towards PE interfaces causing continuous
MAC movements between PE interfaces. Based on the threshold and interval configured, the PE interface with lowest ifindex is
shut down, thereby breaking the loop. As per the enhancement added from Dell Networking OS 9.11.2.0, the PE loop detection
mechanism works based on the control traffic too. The interface learnt first for a MAC address is considered as old interface
and the interface learnt later for the same MAC is considered as the new interface. In case of loop detection the new interface
will be brought down by the PE loop detection module. Also, based on control traffic, the interface receiving self originated
packets will be shut down by the loop detection module. You can specify the threshold value and a time interval for the
maximum number of station moves to prevent loops on a port extender (PE) port using the mac-address-table station-
move threshold number interval seconds command to bring down the line protocol on all active ports in the learned
path, except for the port with the lowest interface index (ifIndex), to prevent a possible loop. When the number of station
moves for a specified MAC address exceeds the configured threshold value in the configured time, a loop is detected on the PE
ports.
To specify the threshold value and timer interval for the maximum number of station move:
1. Enter Configuration mode.
CONFIGURATION mode
Dell(conf)# mac-address-table station-move threshold number interval seconds
● number is the threshold value. The range is from 5 to 50.
After you enter a threshold value, you can specify a time interval in seconds. The range is from 1 to 60 seconds.
Dell(conf)# mac-address-table station-move threshold 5 interval 30
NOTE: Dell Networking OS recommends that you use the command because xSTP protocols are not supported on PEs.
2. If a station move for a MAC address is detected above the configured threshold and within the specified time, a syslog
message is triggered with the port information. All ports on which the station move was detected are shut down, except the
old interface. For example:
Jun 18 09:55:35: %RPM0-P:RP %MACMGR-1-PE LOOP DETECTION: Loop occurred on PE
interfaces:oldInterface: peGigE 0/2/47, newInterface: peGigE 0/1/20,vlanId: 3902,
macAddr: 00:aa:00:00:00:
3. When a PE interface is shut down due to a PE loop detection, you must manually reset it. To reset the interface, shut it
down by entering the shutdown command and then re-enable it by entering the no shutdown command.
4. To display the PE ports that are shut down due to loop detection, enter the show mac learning-limit violate-
action command.
Dell# show mac learning-limit violate-action
Interface Violation-Type Violate-Action Status
PeGi 0/2/47 Pe-Loop Shutdown PEloop-disable
PeGi 100/0/20 Pe-Loop Shutdown PEloop-disable
PeGi 255/0/47 Pe-Loop Shutdown PEloop-disable
Po 1 Pe-Loop Shutdown PEloop-disable
Po 100 Pe-Loop Shutdown PEloop-disable
5. To display the reason why the line protocol is down on a PE port or port channel, enter the show interface command.
EXEC mode
Dell(conf-if-po-1)#do show interface port-channel 1
Port-channel 1 is up, line protocol is down(Pe Loop Detection)
Port Extenders (PEs)
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