Managing a Switch Stack 147
2
The switch has the higher MAC address. 
3
A unit is selected as standby by the administrator, and a fail over action is 
manually initiated or occurs due to stack master failure.
In most cases, a switch that is added to an existing stack will become a stack 
member, and not the stack master. When you add a switch to the stack, one 
of the following scenarios takes place regarding the management status of the 
new switch:
• If the switch has the stack master function enabled but another stack 
master is already active, then the switch changes its configured stack 
master value to disabled.
• If the stack master function is unassigned and there is another stack 
master in the system then the switch changes its configured stack master 
value to disabled.
• If the stack master function is enabled or unassigned and there is no other 
stack master in the system, then the switch becomes stack master. 
• If the stack master function is disabled, the unit remains a non-stack 
master.
If the entire stack is powered OFF and ON again, the unit that was the 
stack 
master
 before the reboot will remain the 
stack master
 after the stack resumes 
operation.
You can manually set the unit number for the switch. To avoid unit-number 
conflicts, one of the following scenarios takes place when you add a new 
member to the stack:
• If the switch has a unit number that is already in use, then the unit that 
you add to the stack changes its configured unit number to the lowest 
unassigned unit number. 
• If the switch you add does not have an assigned unit number, then the 
switch sets its configured unit number to the lowest unassigned unit 
number. 
• If the unit number is configured and there are no other devices using the 
unit number, then the switch starts using the configured unit number. 
• If the switch detects that the maximum number of units already exist in 
the stack making it unable to assign a unit number, then the switch sets its 
unit number to 
unassigned
 and does not participate in the stack.