Stack Changes And Unit Id Assignment - Cisco 500 series Administration Manual

Stack Management

Stack Changes and Unit ID Assignment

NOTE
Stack Changes and Unit ID Assignment
Cisco 500 Series Stackable Managed Switch Administration Guide
• Force Master - If Force Master is activated on a unit, it is selected. If a unit is
forced, it remains forced even after reboot.
• System Up Time -The master-enabled units exchange up time, which is
measured in segments of 10 minutes. The unit with the higher number of
segments is selected as the master. Note: The up time of the backup unit is
retained when it is selected as master in the switch failover process.
• Unit ID - If 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.
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.
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/Disconnecting a Stack Cable
Connecting or disconnecting a stack cable, or configuring a stack port link up or
down, triggers a topology change. This can be the result of adding or removing a
unit from the stack, or from changing the stack topology between a chain and a
ring.
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