Allied Telesis AlliedWare Plus GS980MX Series Installation Manual page 80

Chapter 2: Virtual Chassis Stacking
When switches have the same priority values, they compare their MAC
addresses to select the master switch. As with the priority value, the lower
the MAC address, the higher the priority. The switch with the lowest MAC
address becomes the master switch.
If you power on the stack for the first time without adjusting the priority
values, the master switch is selected based on the MAC addresses if
the units are powered on simultaneously. If you power on the switches
one at a time, the master switch is the first switch to be powered on.
You can set the priority values of the switches either before or after you
build the stack. Changing the values after the stack is operating does not
change the parameter settings of the stack or the ID numbers of the
devices.
It should be noted that the master switch of a stack does not have to have
the ID number 1. It can have any ID number.
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