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24 Introduction
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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 6 can be defined for
stack members.
When the Master unit boots or when inserting or removing a stack member, the Master unit
initiates a stacking 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. One Master 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
ten minute 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.
Each port in the stack has a specific Unit ID, port type, and port number, which are part of both the
configuration commands and the configuration files. Configuration files are managed only from
the device Stack Master, including: