Linksys SLM224G4S manual Merging Two Stacks, Both Stacks Kept Running During Insertion

Appendix B About Switch Stacking

before the split. Since the Backup Master was not acting as a master prior to the split, it will initiate a topology database and port-learning process. Traffic might be halted for a short period of time until synchronization (unit and port configuration) is completed. New units learned by the Backup Master will notify the system administrator (using SYSLOG messages and SNMP traps).

d.In either case (steps b and c above), the subgroup will continue to work as it did before the split, except that the number of units is lower than prior to the split.

e.No unit ID changes are made in either subgroup.

f.Each new stack will have a Master (one has the original Master, the other has the Backup). They thus operate as two separate stacks, both having the same configuration and hence the same IP address.

WARNING: Both resulting stacks will have the same IP Address. This may lead to problems on the network, since there would be no way for users to connect to one of the stacks through its IP address.

Subgroup Contains Neither Master Unit nor Backup Master Unit

Please note that this is exactly the same as the case of a failed master, where no backup is available.

•In this case the units with ID 3-6 (3-4 for SLM248G4S) in this subgroup will not renumber themselves, and will remain shut down until a stack Master enabled unit is connected, and starts to operate as stack master. It is the responsibility of the Master-discovery process to see that the master is gone.

•In this subgroup, the units lose connection with the Master. Since they started as a running stack and none of them are in factory default mode, renumbering will not take place, and even a Reset of the units will not affect unit ID assignment (As noted above, units can be renumbered only by a stack Master).

•No unit ID changes are made in either subgroup.

Again it should be emphasized that none of the units in either half of the stack will renumber themselves.

Merging Two Stacks

In this example, the user would like to merge two working stacks and create one stack out of those two stacks. In this example one should distinguish between two scenarios:

•The incoming units are turned off before insertion and then powered back up afterward

•The two stacks are kept running during the insertion (for example, the stacking cables of the two stacks are connected)

Incoming Units Turned Off Before Insertion, then Turned On After Insertion

This is exactly the same as inserting units into a running stack (refer to “Replacing a Failed Stack Member in a Running Stack”). The only difference is that more than one unit will be inserted into the stack and therefore for each unit inserted to the stack the same process will be executed.

Both Stacks Kept Running During Insertion

If each of the joined stacks has a Master unit, both Master units will perform Master discovery and participate in a Master Election, as described above. One of the Master units will be selected as the Master unit—for the merged stack. The criteria for choosing the master are:

•Force Master

•System Up Time

•Lowest Unit ID

•Lowest MAC

The process of master selection between the two master units is as follows:

•If force master is enabled then the unit which is forced is chosen.

•Up time is measured by quantities of periods of 10 minutes. If the number of 10 minute periods is higher for one of the units then this unit is chosen.

•If both units have the same up time (measured in periods of 10 minutes) the unit with the lowest unit ID is elected.

•If both Master unit IDs are equal the unit with the Lower MAC is chosen.

•The Master unit that loses its“mastership”in the Master election process will be renumbered if the unit ID was dynamically allocated. renumbering will now allocate it a new number by the new Master, as a stack member, or possibly Backup Master. It should be emphasized that in no case will there be two units with the same Unit ID at the end of this process.

•The Master unit that loses its mastership in the Master election process will be shut down if the unit ID was manually allocated. It is recommended that the administrator configure it to auto-assigned Unit ID before reconnecting it to the stack.

24/48-Port 10/100 + 4-Port Gigabit Resilient Clustering Smart Switch with 2 Combo SFPs 56