Alcatel-Lucent OmniSwitch AOS Release 7 - MC-LAG Loop Detection

MC-LAG Overview Configuring Multi-chassis Link Aggregation
page 8-12 OmniSwitch AOS Release 7 Network Configuration Guide March 2011
Basic MC-LAG Principle
MC-LAG Loop Detection
Since the Spanning Tree Protocol is disabled on MC-LAG ports, the MC-LAG feature provides a method
of loop detection in order to detect an invalid network topology. The mechanism provides loop detection
for any potential loops that include a set of MC-LAG aggregate ports.
The loop detection mechanism generates multicast Loop Detect PDU at regular intervals. In a MC-LAG
network, the source MAC is reserved and the MAC is unique to each chassis ID. The multicast PDU is
flooded out on the VFL and MC-LAG primary ports.
Loop Detection is flagged when the PDU is returned to the transmitting peer, causing the following to
occur.
• A log message is sent for loop detect event.
• A SNMP trap is generated, and
• The offending port is shutdown.
Port A
Switch
SW
1
Switch
SW
2
Port B Port C
Port X
The traffic received on Port A
cannot be flooded out Port B
or Port C.