14 IntroductionThe device units are shipped with a default Unit ID of the stand-alone unit. If the device is operating asa stand-alone unit, all stacking LEDs are off.Once the user selects a different Unit ID, it is not erased, and remains valid, even if the unit is reset.Unit ID 1 and Unit ID 2 are reserved for Master enabled units. Unit IDs 3 to 8 can be defined for stackmembers.When the Master unit boots or when inserting or removing a stack member, the Master unit initiatesa stacking discovering process.NOTE: If two members are discovered with the same Unit ID the stack continues to function, however only the unitwith the older join time joins the stack. A message is sent to the user, notifying that a unit failed to join the stack.Removing and Replacing Stacking MembersUnit 1 and Unit 2 are Master enabled units. Unit 1 and Unit 2 are either designated as Master Unit orBackup Master Unit. The stack Master assignment is performed during the configuration process.One Master enabled stack member is elected as Master, and the other Master enabled stack member iselected as Backup Master, according to the following decision process:• If only one Stack Master enabled unit is present, it is elected as the Master.• If two Master enabled stacking members are present, and one has been manually configured as theStack Master, the manually configured member is elected as Stack Master.• If two Master enabled units are present and neither has been manually configured as the Master, theone with the longer up-time is elected as the Stack Master.• If two Master enabled units are present and both have been manually configured as the Master, the onewith the longer up-time is elected as the Stack Master.• If the two Master enabled stacking members are the same age, Unit 1 is elected as the Stack Master.NOTE: Two stacking member are considered the same age if they were inserted within a ten minute interval.For example, Unit 2 is inserted in the first minute of a ten-minute cycle, and Unit 1 is inserted in fifthminute of the same cycle, the units are considered to be the same age. If there are two Master enabledstack members that are the same age, then Unit 1 is elected master.The Stack Master and the Backup Master maintain a Warm Standby. The Warm Standby ensures thatthe Backup Master takes over for the Stack Master if a failover occurs. This guarantees that the stackcontinues to operate normally.During the Warm Standby, the Master and the Backup Master are synchronized with the staticconfiguration only. When the Stacking Master is configured, the Stack Master must synchronize theStacking Backup Master. The Dynamic configuration is not saved, for example, dynamically learnedMAC addresses are not saved.
