Managing Device Information
Managing Stacking
Cisco Small Business SFE/SGE Managed Switches Administration Guide 17
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Unit ID as the switch being replaced. The newly inserted switch is identified by the
Master unit by its Unit ID. Since the configuration of the original switch is also
stored in the Master and Backup units by Unit ID, the new switch automatically
receives the configuration of the old switch. This eliminates the need to configure
the new switch and reduces the system downtime.
The advantage of manual vs. automatic unit numbering is illustrated in the
following example:
A stack consists of Units 1,2,4,6,7. Unit 7 fails and an identical replacement unit is
inserted. If the replacement unit is manually pre-set to be Unit 7, it can be inserted
into the stack and inherit the configuration of the replaced (failing) Unit 7. However,
if the replacement unit is not preset but is inserted in factory default mode (Unit 0),
it is automatically renumbered to Unit 3 because that is the lowest available Unit ID
in the stack. The new Unit 3 now inherits the previous unit 3 configuration.
Otherwise, the system administrator must manually configure all the ports of the
new Unit 3.
Unit ID Conflict Resolution
If two or more stacking members have the same valid Unit ID, the Master attempts
to resolve the conflict by awarding the contested Unit ID to one of the units. For
stacking members that are not granted the unit ID, the Stacking Master either:
• Automatically resets the Unit ID to 0. The Stacking members become eligible to
be reassigned another Unit ID by Automatic Unit ID Assignment.
• The units are shut down. A unit that is automatically shut down remains
powered on, but it is not operational, indicated by the solid red port Led. It is
not a member of the stack and its connections are effectively disconnected
from its immediate neighbors in the stack. If the stack is initially connected in a
ring topology, the shutdown unit changes the topology into a chain. However, if
the stack is initially configured in a chain topology, the shutdown unit breaks the
chain. Depending on the particular configuration, may lead to other units being
shut down. An automatically shut down unit remains shut down until the system
administrator, manually renumbers the stacking member or removes the
stacking member from the stack. A message is sent to the user that a unit failed
to join the stack.
The Master unit attempts to resolve Unit ID conflicts by applying the following
rules:
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