Appendix B | About Switch Stacking |
•If the incoming unit did not have an assigned Unit ID (that is, it was in factory default mode), it will be assigned the lowest available Unit ID by the Master. It is strongly recommended that automatic assigned unit ID mode be used since it provides better resiliency to the stack.
•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
3.The stack Master will now carry out Unit and port 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.
If the incoming unit is identical in makeup to the replaced unit, the entire configuration of the replaced unit will be applied to the incoming one and the stack will go back to the state it was in before unit failure. However, sometimes the incoming unit is not identical to the unit that failed in these cases. The stack Master will apply the configuration in the following manner:
•If a
(Note that the configuration of all 48 ports of the failed unit is remembered, even though only the first 24 are currently applied. If, in the future, a 48 port unit is inserted and assigned the same Unit ID, it will be configured as the original failed 48- port unit was configured).
•If a
•If the units (the failed one and its replacement) had/have uplink ports, then the first uplink of the incoming unit will be configured as was the first uplink of the failed unit, and so on.
Stack Master Failure and Replacement
In this example, the 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 Backup Master detects (via the ongoing monitoring Master Discovery process) that the master unit no longer responds and takes over as the stack master. The backup master directs all other stack members to route
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 will perform Master discovery, and perhaps participate in a Master Election, as described above.
•If the incoming unit has a Unit ID of 1 or 2 (that is, the unit is a
2.The stack Master at this stage will carry out a Unit ID allocation and conflict resolution process.
•If the incoming unit did not have an assigned Unit ID (that is, it was in factory default mode), it will be assigned the lowest available Unit ID by the Master. It is strongly recommended that automatic assigned unit ID mode be used since it provides better resiliency to the stack.
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