User Controls; Stacking Examples; Replacing A Failed Stack Member In A Running Stack - Cisco Gigabit Smart Switch with Resilient Clustering Technology and PoE SLM224G4PS User Manual

Appendix B
If both duplicate units are in auto (self ordering) mode,
•
then the unit ID will be decided by the Mac address.
The unit with the lower Mac will keep its unit ID. The
other will be reassigned a new unit ID.
If one of the duplicates is in auto (self ordering)
•
mode and the other unit is in manual mode then the
manual mode unit will keep its ID and the other will be
reassigned a new unit ID.
If both duplicate units are in manual mode then both
•
of them will be shut down.
If the stack Master is able to allocate a unique Unit ID to
each unit, then all units can operate as a stack. If the stack
Master is unable to allocate a Unit ID to any unit, that unit
is effectively shut down and will not participate in the
stack.
In particular, units with a conflicting manually set Unit ID
number will be shut down because the Master cannot
override the system administrator's assignment to resolve
the conflict.
If there are more units than the maximum number allowed
in a stack and the incoming units are already in factory
default state (which means they do not have unit ID
assigned) then a Master will be elected following Master
Discovery and Master Election processes. All other units
will remain shut down. Please note that in some extreme
cases, due to a race condition during the boot process,
some of the units might be connected and join the stack..
If the incoming units already have a unit ID then none of
them will join the stack and all will be left in shutdown
mode (since there is no way to know which of them are
preferable).
NOTE:
If a unit is shut down, its stacking
links will be inactive. Moreover, if the stacking
units are connected in a chain topology, the
shutdown of one unit breaks the chain and may
cause other units to be shut down if they have
no active link to the Master unit.
Unit and Port Configuration
At this point, each unit in the stack has a unique Unit-ID;
one of the units is the stack Master, and, possibly, one of
the units serves as Backup Master. The stack Master will
now configure each of the member units and its ports
according to the configuration file present on the Master.
If the stack has a Backup Master the configuration file will
also be copied to the Backup Master.
Once all the units and ports are configured, the stack will
go into normal operational mode. If any change is made
to the system configuration, the change will be stored by
24/48-Port 10/100 + 4-Port Gigabit Smart Switch with Resilient Clustering Technology and PoE
About Switch Stacking
the stack Master and will be copied to the Backup Master
(if it exists).

User Controls

Using either the CLI or the graphical user interface (GUI),
the user can configure the following settings:
Set the operational mode of the unit (which will take
•
effect after next reboot) – Standalone or Stack.
Force a unit to be the stack Master after the next reset
•
Assign a static Unit ID, or, allow the unit to be
•
renumbered.

Stacking Examples

Replacing a Failed Stack Member in a Running
Stack
In this example, a non-master unit fails in a running stack.
When notified of the failure, a system administrator
removes the failed unit and replaces it with another one.
When the unit fails, the stack Master detects (via the
ongoing Master Discovery process) that the unit no longer
responds, and directs all other stack members to route
unit-to-unit traffic around the failed unit using the ring
topology of the stacking connections. At the same time
the stack Master notifies the system administrator (using
SYSLOG messages and SNMP traps) of the failure.
When the failed unit is disconnected from the stack, all
traffic will already be routed around it, and as long as all
other stacking connections are left intact, the stack should
continue to run.
When a new unit is inserted in the stack and powered up,
the following will happen:
1. The incoming unit, being in stack mode, will perform
Master discovery, and perhaps participate in a Master
Election, as described above for any stacking-mode
unit powering up.
If the incoming unit has a Unit ID of 1 or 2, i.e. it
•
is a master enabled unit, it will initiate a Master
Election. However, since the running stack Master
has a longer run time, it will remain elected as
the stack Master and the incoming unit will not
become a new stack Master.
If the incoming unit has a Unit ID of 3 to 6 (3 to 4 for
•
SLM248G4PS), it will try to become a member unit
of the stack subject to the already running stack
Master, and Master Election will not take place.
The stack Master at this stage will carry out a Unit ID
2.
allocation and conflict resolution process.
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