Merging Independent Stacks - Lenovo RackSwitch G8264 Application Manual

Merging Independent Stacks

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If multiple stack links or stack Member switches fail, thereby separating the Master
and Backup into separate sub‐stacks, the Backup automatically becomes an active
Master for the partial stack in which it resides. Later, if the topology failures are
corrected, the partial stacks will merge, and the two active Masters will come into
contact.
In this scenario, if both the (original) Master and the Backup (acting as Master) are
in operation when the merger occurs, the original Master will reassert its role as
active Master for the entire stack. If any configuration elements were changed and
applied on the Backup during the time it acted as Master (and forwarded to its
connected Members), the Backup and its affected Members will reboot and will be
reconfigured by the returning Master before resuming their regular roles.
However, if the original Master switch is disrupted (powered down or in the
process of rebooting) when it is reconnected with the active stack, the Backup
(acting as Master) will retain its acting Master status to avoid disruption to the
functioning stack. The deferring Master will temporarily assume a role as Backup.
If both the Master and Backup are rebooted, all member switches in the stack will
also reboot. When the switches resume operation, they will assume their originally
configured roles.
If, while the stack is still split, the Backup (acting as Master) is explicitly
reconfigured to become a regular Master, then when the split stacks are finally
merged, the Master with the lowest MAC address will become the new active
Master for the entire stack.
If switches from different stacks are linked together in a stack topology without
first reconfiguring their roles as recommended, it is possible that more than one
switch in the stack might be configured as a Master.
Although all switches which are configured for stacking and joined by stacking
links are recognized as potential stack participants by any operational Master
switches, they are not brought into operation within the stack until explicitly
assigned (or "bound") to a specific Master switch.
Consider two independent stacks, Stack A and Stack B, which are merged into one
stacking topology. The stacks will behave independently until the switches in
Stack B are bound to Master A (or vice versa). In this example, once the Stack B
switches are bound to Master A, Master A will automatically reconfigure them to
operate as Stack A Members, regardless of their original status within Stack B.
However, for purposes of future Backup selection, reconfigured Masters retain
their identity as configured Masters, even though they otherwise act as Members.
In case the configured Master goes down and the Backup takes over as the new
Master, these reconfigured Masters become the new Backup. When the original
configured Master of the stack boots up again, it acts as a Member. This is one way
to have multiple backups in a stack.
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Chapter 18: Stacking