Priority Numbers - Allied Telesis SwitchBladex8112 Installation Manual

Priority Numbers

Section III: Building a Stack with VCStack Plus
SwitchBlade x8112 Chassis Switch and AT-SBx81CFC960 Card Installation Guide
The switches of the stack perform an initialization procedure whenever
they are reset or powered on. During the process, which involves
activating the management software and forming the stack, the units
select the active master controller card. This card is responsible for
maintaining the configuration file that contains the parameter settings for
all the devices in the stack and for periodically sharing the configuration
file with the other controller cards.
The stack can have only one active master controller card. The other
cards are referred to as standby master controller cards. If, for instance,
the stack has four controller cards, one of the cards acts as the active
master card and the other three function as standby master cards.
Standby master controller cards are not inactive. Rather, they forward
traffic between the Ethernet line cards on the backplanes of their chassis
and manage traffic on their SFP+ slots and the stack trunk.
The method by which the controller cards select the active master
controller card depends on whether the switches are rebooted
simultaneously or one after the other.
If the switches are powered on or reset simultaneously, the controller
cards use the following values to select the active maters controller card
for the stack:
 Slot numbers
 Priority numbers
 MAC addresses
At the start of the selection process, the switches, if they both have two
controller cards, select an active card for their respective chassis, by slot
number. In most cases, preference is given to the controller card in slot 5.
After each switch has selected an active controller card, the two active
cards in the switches communicate over the stack trunk to select the active
master controller card for the entire stack. To accomplish this, they first
compare their priority numbers. The number has a range of 0 to 255. The
default is 128. The lower the number, the higher the priority. If one of the
controller cards has a lower priority number, it becomes the active
controller card for the stack and the other card is placed in the standby
master mode, along with the other controller cards.
If the controller cards have the same priority number, they compare their
MAC addresses. The controller card with the lower MAC address
becomes the active master controller card for the stack.
Setting the priority number during the stack configuration procedure is
301