Cisco SGE2000 - - Gigabit Switch Administration Manual page 27

Managing Device Information
Managing Stacking
STEP 1
STEP 2
STEP 3
STEP 4
STEP 5
STEP 6
Cisco Small Business SFE/SGE Managed Switches Administration Guide
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.
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.
Two manually numbered units with the same Unit ID can never be added or
inserted into a stack simultaneously. Both units are shut down.
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.
Connecting more than the maximum number (eight) of units in a new stack may
produce unpredictable results due to race conditions among the units.
Any units that have been reset to Unit ID 0 are then reassigned new Unit IDs, if
possible, by Automatic Unit ID Assignment.
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