Merging Independent Stacks - Lenovo Flex System Fabric CN4093 Application Manual

Merging Independent Stacks

© Copyright Lenovo 2015
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.
Note: When the Backup becomes a Master, if NTP is enabled from the CMM,
configuration changes are made to the Backup (acting as Master) by the CMM.
Therefore, in the event of a subsequent merger, the aforementioned reboot and
reconfiguration of the Backup and its affected Members will occur.
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, the switches 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.
Since up to 16 units can be attached to a stack, a merge between two 8 unit stack
can be performed. The user will then have to choose which units will remain in the
final stack and which will be eliminated, since only 8 of them can forward
networking traffic, the rest having the data links disabled.
Note: Do not merge hybrid stacks if the total number of CN4093 switches exceeds
two units.
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.
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Chapter 14: Stacking