14 Introduction
The device units are shipped with a default Unit ID of the stand-alone unit. If the device is operating as
a 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 stack
members.
When the Master unit boots or when inserting or removing a stack member, the Master unit initiates
astacking discovering process.
NOTE: If two members are discovered with the same Unit ID the stack continues to function, however only the unit
with 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 Members
Unit 1 and Unit 2 are Master enabled units. Unit 1 and Unit 2 are either designated as Master Unit or
Backup Master Unit. The stack Master assignment is performed during the configuration process.
OneMaster enabled stack member is elected as Master, and the other Master enabled stack member is
elected 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 the
Stack 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, the
one 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 one
with 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 tenminute interval.
For example, Unit 2 is inserted in the first minute of a ten-minute cycle, and Unit 1 is inserted in fifth
minute of the same cycle, the units are considered to be the same age. If there are two Master enabled
stack 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 that
the Backup Master takes over for the Stack Master if a failover occurs. This guarantees that the stack
continues to operate normally.
During the Warm Standby, the Master and the Backup Master are synchronized with the static
configuration only. When the Stacking Master is configured, the Stack Master must synchronize the
Stacking Backup Master. The Dynamic configuration is not saved, for example, dynamically learned
MAC addresses are not saved.