Administration: Stack Management
Stack Changes
Cisco 500 Series Stackable Managed Switch Administration Guide Release 1.3 66
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• Unit ID—f both units have the same number of time segments, the unit with
the lowest unit ID is selected.
• MAC Address—If both units IDs are the same, the unit with the lowest MAC
address is chosen.
NOTE For a stack to operate, it must have a master unit. A master unit is defined as the
active unit that assumes the master role. The stack must contain a unit 1 and/or unit
2 after the master selection process. Otherwise, the stack and all its units are
partially shut down, not as a complete power-off, but with traffic-passing
capabilities halted.
Stack Changes
This section describes various events that can cause a change to the stack. A
stack topology changes when one of the following occurs:
• One or more units are connecting and/or disconnecting to and from the
stack.
• Any of its stack ports has a link up or down.
• The stack changes between ring and chain formation.
When units are added or removed to and from a stack, it triggers topology
changes, master election process, and/or unit ID assignment.
Connecting a New Unit
When a unit is inserted into the stack, a stack topology change is triggered. The
unit ID is assigned (in case of auto numbering), and the unit is configured by the
master.
One of the following cases can occur when connecting a new unit to an existing
stack:
• No duplicate unit IDs exist.
- Units with user-defined IDs retain their unit ID.
- Units with automatically-assigned IDs retain their unit ID.
- Factory default units receive unit IDs automatically, beginning from the
lowest available ID.
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