Cisco SGE2000 Administration Manual page 23

Linksys One Ready Communications Solution
3
Master Discovery Process
When a unit in stack mode initializes, its behavior depends on its Unit ID (if one is
configured):
• If the unit does not have a current Unit ID (that is, the unit is in factory default mode)
and if there is a Stack Master, the unit is allocated a Unit ID number from the Stack
Master. If there is no Stack Master, then the unit participates in the Master Election
process, and may be chosen as the new Stack Master or Backup Master.
• If the unit's current Unit ID is 1 or 2 (that was previously allocated, even if used in a
different stack), then the unit participates in the Master Election process.
• If the unit has a current Unit ID (that was previously allocated, even if used in a
different stack), the unit tries to act according to its Unit ID number in the new stack.
For example, if the unit's current Unit ID is 3 through 8, it will try to connect to the
running Stack Master, and will not proceed to the next stage until contact with the
Stack Master is made. These units will not participate in the Master Election process,
and if no Stack Master is present, the units are effectively shut down.
The Stack Master and all other stack units carry out a continuous process of Master
Discovery by frequently exchanging stack control messages. This allows units to know if
another unit fails or becomes unreachable.
Master Election Process
When units in stacking mode initialize, one of the units is elected as the Stack Master. If a
unit in the stack was set to "Force Master" by the system administrator, that unit is elected as
the Stack Master. Only master-enabled stack units (for example, those with the Unit ID of 1
or 2) can be configured as "Force Master."
If the stack contains units whose unique Unit ID is 1 or 2, then one of these two units will be
the Stack Master. It does not matter if the Unit ID was originally assigned automatically or
manually. These units are called master-enabled units. If there is only one master-enabled
unit, it will be elected as the Stack Master (even if its Unit ID is 2).
If there are two master-enabled units, the two units decide which of them is the Master by
checking which one has been running for a longer time (in intervals of 10 minutes). The unit
that has been running for the longer time will be the Stack Master. If they have been running
for the same amount of time, the unit with the Unit ID of 1 will be the Stack Master. If both
Chapter 3: Connecting the Switch
Understanding Advanced Stacking
18