Administration: Stack Management
Types of Units in Stack
73 Cisco 500 Series Stackable Managed Switch Administration Guide
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destination using the remaining stacking links. During Fast Stack Link
failover, the master/backup units remain active and functioning.
NOTE The Fast Stack Link Failover feature is only active for one or two
unit stacks. See Stack Port Link Aggregation.
Types of Units in Stack
A stack consists of a maximum of eight units. A unit in a stack is one of the
following types:
• Master—The master unit’s ID must be either 1 or 2. The stack is managed
through the master unit that manages itself, the backup unit and the slave
units.
• Backup—If the master unit fails, the backup unit assumes the master role
(switchover). The backup unit’s ID must be either 1 or 2.
• Slave—These units are managed by the master unit.
In order for a group of units to function as a stack, there must be a master-enabled
unit. When the master-enabled unit fails, the stack continues to function as long as
there is a backup unit (the active unit that assumes the master role).
If the backup unit fails, in addition to the master, and the only functioning units are
the slave units, these also stop functioning after one minute. This means for
example, that if after 1 minute, you plug in a cable to one of the slave units that was
running without a master, the link will not come up.
Backward Compatibility of Number of Units in Stack
Previous versions of the device supported a maximum of four units as opposed to
the current version that supports eight units. Upgrading from earlier software
releases can be done without changing the configuration files.
When a firmware version, which does not support the hybrid stack modes is
loaded to the stack and the stack is rebooted, the stack reverts to Native Stack
mode. When a device in Hybrid stack mode is loaded with a firmware version that
does not support Hybrid stack mode, its system mode reverts to the default
system mode (SG500X/EWS2-550X: L3 and L2, Sx500: L2).
If a stack’s unit IDs were manually-configured, those units whose ID is greater than
4 are switched to auto numbering.
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