Master Selection Process; Stack Changes - Cisco 500 Series Administration Manual

Administration: Stack Management

Master Selection Process

Master Selection Process
NOTE

Stack Changes

Cisco 500 Series Stackable Managed Switch Administration Guide
The master unit is selected from the master-enabled units (1 or 2). The factors in
selecting the master unit are taken into account in the following priority:
• Force Master—If Force Master is activated on a unit, it is selected.
• 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. If both units have the same number of time segments,
and the unit ID of one of the units was set manually while the other unit's unit
ID was set automatically, the unit with the manually-defined unit ID is
selected; otherwise the unit with the lowest unit ID is selected. If both units
IDs are the same, the unit with the lowest MAC address is chosen. 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.
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