Specifications

Chapter 6. IBM Virtual Fabric 10Gb Switch Module implementation 243
If multiple stack links or stack Member switches fail, and separate the Master and Backup into
separate substacks, the Backup automatically becomes an active Master for the partial stack
in which it is. Later, if the topology failures are corrected, the partial stacks merge, and the
two active Masters 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 reasserts its role as active Master for
the entire stack. If any configuration elements are changed and applied on the Backup during
the time it acted as the Master (and forwarded to its connected Members), the Backup and its
affected Members reboot and are 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) retains
its acting Master status to avoid disruption to the functioning stack. The original Master
temporarily assumes a role as a Backup.
If both the Master and Backup are rebooted, the switches assume their originally
configured roles.
If, while the stack is still split, the Backup (acting as Master) is reconfigured to become a
regular Master, then when the split stacks are finally merged, the Master with the lowest MAC
address becomes the new active Master for the entire stack.
Merging independent stacks
If switches from different stacks are linked together in a stack topology without first
reconfiguring their roles, it is possible that more than one switch in the stack might be
configured as a Master.
Consider two independent stacks, Stack A and Stack B, which are merged into one stacking
topology. The stacks behave independently until the switches in Stack B are bound to Master
A (or vice versa). In this example, after the Stack B switches are bound to Master A, Master A
automatically reconfigures them to operate as Stack A Members, regardless of their original
status within Stack B.
However, for future Backup selection purposes, reconfigured Masters retain their identity as
configured Masters, even though they otherwise act as Members and lose all settings that
pertain to their original stacks.
Backup switch selection
An operational stack can have one optional Backup at any time. Only the Backup specified in
the active Master’s configuration is eligible to take over current stack control when the Master
is rebooted or fails. The Master automatically synchronizes configuration settings with the
specified Backup to facilitate the transfer of control functions.
The Backup retains its status until one of the following occurs:
򐂰 The Backup setting is deleted or changed from the active Master.
򐂰 A new Master assumes operation as the active Master in the stack, and uses its own
configured Backup settings.
Important: Although all switches that 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 assigned (or “bound”) to a specific
Master switch.