Replacing A Failed Stack Master Unit In An Operational Stack - Cisco SGE2000 Administration Manual

Linksys One Ready Communications Solution
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Replacing a Failed Stack Master Unit in an Operational Stack

When the Stack Master unit fails, the stack Backup Master, using the Master Discovery
process, discovers that the Stack Master unit no longer responds. The Backup Master takes
over as the Stack Master. The Backup Master (now the Stack Master) directs all other stack
members to route unit-to-unit traffic around the failed unit using the ring topology of the
stacking connections. Concurrently, the Backup Master notifies the system administrator of
the failure by sending SYSLOG messages and SNMP traps.
Because all traffic has been routed around the failed unit, when it is disconnected from the
stack, the stack continues to run as long as all other stacking connections are left intact.
When a new unit is inserted in the stack and powered on, the following occurs:
1. The incoming unit, which is in stack mode, performs the Master Discovery process, and
may participate in the Master Election process.
• If the incoming unit has a Unit ID of 1 or 2 (it is a master-enabled unit) it initiates the
Master Election process. However, because the running stack Backup Master has a
longer runtime (if it has been running for more than 10 minutes) it remains the Stack
Master and the incoming unit does not become the new Stack Master. This can cause
an incoming unit with a Unit ID of 1 to serve as the stack Backup Master, while the
current unit with the Unit ID of 2 remains the active Stack Master.
2. The Stack Master performs Unit ID allocation and the conflict resolution process.
• If the incoming unit did not have an assigned Unit ID (that is, it is in factory default
mode), it is assigned the lowest available Unit ID by the Stack Master. We
recommend that you use the automatically-assigned unit ID mode because 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 keeps its assigned Unit ID and the Stack Master
applies any configuration relevant to that Unit ID to the incoming unit.
• If the incoming unit already has an assigned Unit ID, and that Unit ID conflicts with a
unit ID in the current stack, the Stack Master allocates a new Unit ID to the incoming
unit, giving it the lowest available Unit ID. However, if the incoming unit has a
manually assigned Unit ID, the Stack Master cannot change it. If the incoming unit
cannot be assigned an available Unit ID, then it is shut down and is not joined to the
stack.
Chapter 3: Connecting the Switch
Stack Troubleshooting and Maintenance
26