Allied Telesis AlliedWare Plus Operating System Version 5.4.4C (x310-26FT,x310-26FP,x310-50FT,x310-50FP) - Manual (Page 2128)

VCStack Introduction
Software Reference for x310 Series Switches
82.14 AlliedWare Plus TM Operating System - Version 5.4.4C C613-50046-01 REV A
Stack Separation and Recovery
Stack stubs occur when a fault results in the stack splitting into two, with one of the stack
members taking on the role of stack master. Where the stack master is still active after a
fault, and other stack members are not aware that the stack master is still active, the result
can be two independently operating stacks, or stubs.
When two stub stacks are reconnected, a dual master situation will be detected, and the
console log will display the message that a ‘duplicate master’ was detected. This situation
results in the re-election of the stack master based upon the lowest Priority ID, or, where
both members have the same Priority ID, the lowest MAC address. The ‘losing’ master and
other prospective stack members will then reboot and join the new stack as backup stack
members.
Stack Maintenance
Adding a stack member
An unstacked switch can be added to an existing stack (hot-swapped in) with minimal
impact on traffic. To do this, power down the new member switch, then connect its
stacking ports and power on the switch. The switch will boot as a member of the stack.
Replacing a stack member
A stack member can be removed from a stack (hot-swapped out) with minimal impact on
stack traffic. To do this, power-down the stack member, and disconnect its stacking ports.
Insert the new stack member, reconnect the stacking ports and power-up the new stack
member.
You can seamlessly swap a stack member switch into the stack to replace another with the
same configuration. This provides a simple way to replace an out-of-service switch with
minimal impact, and minimal administration requirement. You should configure the
replacement switch with the same member ID as its replacement prior to inserting it into
the stack.
Note Stubs are unlikely to cause network connectivity problems if a resiliency link is
used.
Note The existing Stack Member-ID and the device MAC address will have no effect
on the status of the new member switch. The stack will admit the new device as
an ordinary stack member and allocate it a new Stack Member-ID if its ID is one
that already exists.
However, for good practice we recommend pre-configuring the new member
with settings that are appropriate for when the new switch becomes a stack
member.
This is to avoid unexpected situations occurring when the stack is rebooted.
For example, if the new member had a priority setting that was lower than 128
and all the existing stack members were configured with the default; then,
when the stack is rebooted, the new member would be elected as the stack
master.