Lenovo Flex System Fabric CN4093, Application Manual

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CN4093 Application Guide for N/OS 8.4
Splitting and Merging One Stack
If stack links or Member switches fail, any Member which cannot access either the
Master or Backup is considered isolated and will not process network traffic (see
“No Backup” on page 239 ). Members which have access to a Master or Backup (or
both), despite other link or Member failures, will continue to operate as part of
their active stack. A Member that is isolated due to link failure resets itself. After it
is up, if the link failure still exits, the Member stays in isolated state keeping all its
data links disabled. Only the management and stacking links are enabled. If the
Member was not configured when it went to isolated state, the Master pushes the
configuration when the Member joins back the stack.
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, 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.