Splitting A Stack - Cisco Gigabit Smart Switch with Resilient Clustering Technology and PoE SLM224G4PS User Manual

Appendix B
If the incoming unit already has an assigned Unit ID,
•
and that Unit ID is unused in the current stack, the
incoming unit will keep its assigned Unit ID and the
Master will apply to it any configuration relevant to
that Unit ID.
If the incoming unit already has an assigned Unit
•
ID, and that Unit ID conflicts with a unit ID in the
current stack, the Master will reallocate a new
Unit ID to the incoming unit, giving it the lowest
available Unit ID (assuming, of course, that the
incoming unit does not have a manually assigned
Unit ID, which the Master cannot change).
If the incoming unit cannot be assigned an
•
available Unit ID for any reason (in the case of unit
replacement that can only happen if the incoming
unit has a manually assigned Unit ID), then it will be
effectively shut down—that is, it will not be joined
to the stack.
The stack Master will now carry out Unit and port
3.
configuration for the incoming unit.
Any configuration information the Master has that
•
is relevant to the number assigned to the incoming
unit will be applied. In particular, if the incoming
unit was assigned the same Unit ID of the unit it
replaces, then it will receive the same configuration
as the failed unit, to the extent possible, as
described in section "Replacing a Failed Stack
Member in a Running Stack" above.

Splitting a Stack

In this example, let us assume that a working stack is
split into two groups, either by failure of a stacking link
connecting two units in the stack or by a failed unit in a
chain topology which causes disconnection between two
units in the stack. In this case we should consider each
subgroup as an independent running stack configuration.
For each subgroup three suboptions will be considered:
Both the Master unit and the Backup master unit are
•
part of the subgroup.
Either the Master unit or the Backup master unit are
•
part of the subgroup.
Neither the Master unit nor the Backup Master unit are
•
part of the subgroup.
The following describes what happens within each
subgroup for each of these three suboptions.
Subgroup Contains Both Master Unit and Backup Master Unit
Nothing changes, except the master sees the missing
•
units as having been removed, and routes traffic
around them, as described in section "Replacing a
Failed Stack Member in a Running Stack" above.
24/48-Port 10/100 + 4-Port Gigabit Smart Switch with Resilient Clustering Technology and PoE
About Switch Stacking
Since this subgroup contains both master and backup,
•
the subgroup works, and the other subgroup will not
work. Refer to step 3 below for detailed information.
The sequence of actions is as follows:
•
a. The Master Discovery, Master Election and Unit ID
Allocation & Duplicate Unit ID Conflict Resolution
processes will be executed.
b. Any configuration information that the Master
has that is relevant to the units remaining in the
subgroup will remain unchanged.
c. Topology information (the information for each
unit on how to send traffic to any other unit in the
stack) managed by the master will include only
units that are reachable (connected) following the
split.
d. The subgroup continues to work as before, except
that the number of the unit is lower than prior to
the split.
e. No unit ID changes are made in either subgroup.
f. The Master notifies the system administrator (using
SYSLOG messages and SNMP traps) of the removed
units and ports which belong to the unreachable
units and will be reported as 'not present' .
Subgroup Contains Either Master Unit or Backup Master Unit
If the Master unit remains in this subgroup,
•
this is the same
"Replacing a Failed Stack Member in a Running
Stack" above. If the Backup Master unit remains in
this subgroup, then this is the same as section "Stack
Master Failure and Replacement" above.
It should be emphasized that if the stack is split into
•
two parts, one with the master and one with the
backup, both parts will work.
The sequence of actions is as follows:
•
a. The Master Discovery, Master Election and Unit ID
Allocation & Duplicate Unit ID Conflict Resolution
processes will be executed.
b. If the subgroup contains the Master unit, the
stack Master notices (using the master detection
process) that some units no longer respond. At
the same time the stack Master notifies the system
administrator (using SYSLOG messages and SNMP
traps) of the removed units and ports which belong
to the unreachable units and will be reported as
'not present' .
c. If the subgroup contains the Backup Master unit,
the Backup Master will see as a case of Master
failure and take over and manage the remaining
units as a stack, while keeping its number as it was
as described in section
56