Dell PowerConnect 55xx Systems User Guide 47Stack TopologyThe PowerConnect 5500 series systems operates in a ring or chain topology.Ring TopologyIn a ring topology all units in the stack are connected to each other, forming acircle. Each unit in the stack accepts data and sends it to the unit to which itis attached. The packet continues through the stack until it reaches itsdestination. The system discovers the optimal path on which to send traffic.Figure shows units of a stack connected in a ring topology.Stacking Failover Topology - Chain TopologyDifficulties occur when a unit in the ring becomes non-functional, or a link issevered. In this case, the system automatically switches to a chain topology,without any system downtime.In chain topology, each unit in the stack is connected to neighboring unitexcept for the last unit, which is not connected to any other unit.In the chain topology, the stack continues to function as long as there is amaster- or backup-enabled unit in each segment of the stack.When the ring topology is switched to chain topology, an SNMP message isautomatically generated, but no stack management action is required. Theunit that failed must be repaired to restore full stacking operation in the ringtopology.After the stacking issues are resolved, the units can be reconnected withoutinterruption, and the ring topology is restored.Stack Members and Unit IDsThis section describes how to configure the stack.It contains the following topics:• Adding a Unit to the Stack• Assigning Unit IDs• Selecting the Master and Master Backup Units• Switching from the Master to the Master Backup• Replacing Stacking Members
