Cisco 500 series Administration Manual page 73

Stack Management
Stack Changes and Unit ID Assignment
Cisco 500 Series Stackable Managed Switch Administration Guide
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 configuration is
downloaded from 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.
• One or more duplicate unit IDs exist. Auto numbering resolves conflicts and
assigns unit IDs. In case of manual numbering, only one unit retains its unit ID
and the other(s) are shutdown.
• The number of units in the stack exceeds the maximum number of units
allowed. The new units that joined the stack are shut down, and a
notification is sent to the SYSLOG server.
The following shows an example of auto numbering when a master-enabled unit
joins the stack. There are two units with unit ID = 1. The master selection process
selects the best unit to be the master unit (it had been booted longer than the
original one). The other unit is made the backup.
Auto-numbered Master-enabled Unit
The following shows an example of auto numbering when a new unit joins the
stack. The existing units retain their ID. The new unit receives the lowest available
ID.
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