Managing Device Information
Managing Stacking
Cisco Small Business SFE/SGE Managed Switches Administration Guide
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2
STEP 1
When inserting a unit into a running stack, units that are members of the existing
stack retain their Unit IDs. Therefore:
•
If an automatically numbered unit was inserted into a running stack, the
existing unit retains its Unit ID and the newer unit is reset to Unit ID=0.
•
If a manually numbered unit was inserted into a running stack, the existing
unit retains its Unit ID and the manually numbered unit is shut down because
its Unit ID cannot be changed automatically.
STEP 2
When adding a unit to a stack at stack reset (boot), units with duplicate Unit IDs
contend with each other for the same Unit ID according to the rules and
restrictions imposed upon their unit class.
•
Master-enabled units with duplicate Unit IDs compete with each other in the
Master Election.
•
If two units are contending for the same Unit ID, the Master decides as
follows:
-
If one unit is manually numbered and the other unit is automatically
numbered, the manually numbered unit retains its Unit ID and the
automatically numbered unit is reset to Unit ID=0.
-
If both units are automatically numbered, the unit with the lower MAC
address retains its Unit ID and the other unit is reset to Unit ID=0.
-
If both units are manually numbered, the unit with the lower MAC
address retains its Unit ID and the other unit is shut down.
STEP 3
Two manually numbered units with the same Unit ID can never be added or
inserted into a stack simultaneously. Both units are shut down.
STEP 4
When inserting new units into a running stack, if the resulting total number of old
and new units exceeds the maximum allowed (eight), all the new units are shut
down.
STEP 5
Connecting more than the maximum number (eight) of units in a new stack may
produce unpredictable results due to race conditions among the units.
STEP 6
Any units that have been reset to Unit ID 0 are then reassigned new Unit IDs, if
possible, by Automatic Unit ID Assignment.
