Linksys SGE2000 Cisco SGE2000, SGE2000P Gigabit Ethernet Switch Reference Guid - Page 31

Chapter SGE2000/SGE2000P Gigabit Ethernet Switch Reference Guide 2 • If a 48-port unit replaces a 24-port unit, then the first 24 ports of the incoming unit are configured according to configuration of the ports of the failed unit. The remaining ports of the incoming are configured according to the default settings. • If the units have uplink ports, then the first uplink port of the incoming unit is configured according to the configuration of the first uplink port of the failed unit. 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 2: Managing Device Information 23 Stack Troubleshooting and Maintenance