D-Link xStack DXS-3250E Web/Installation Manual page 71

DXS-3227, DXS-3227P, DXS-3250 and DXS-3250E EWS User Guide
Figure 33: Stacking Ring Topology
Most difficulties incurred in Ring topologies occur when a device in the ring becomes non-functional, or a link is
severed. In a stack, the system automatically switches to a Stacking Failover topology without any system down-
time. An SNMP message is automatically generated, but no stack management action is required. However, the
stacking link or stacking member must be repaired to ensure the stacking integrity.
After the stacking issues are resolved, the device can be reconnected to the stack without interruption, and the
Ring topology is restored.
Chain Topology
In a chain topology, there are two units that have only one neighbor. Every unit has an uplink neighbor and a
downlink neighbor. The chain topology is less robust than the ring topology. A failure in the chain results in a topol-
ogy change to the stack. The location of the failure determines the severity of this topology change. The chain
topology also acts as a fail-safe for the ring topology. When the ring topology fails, the stack automatically reverts
to the chain topology.
Stacking Failover Topology
If a failure occurs in the stacking topology, the stack reverts to Stacking Failover Topology. In the Stacking Failover
topology, devices operate in a chain formation. The Stacking Master determines where the packets are sent. Each
unit is connected to two neighboring devices, except for the top and bottom units.
Stacking Members and Unit ID
Stacking Unit IDs are essential to the stacking configuration. The stacking operation is determined during the boot
process. The Operation Mode is determined by the Unit ID selected during the initialization process. For example,
if the user selected stand-alone mode, the device boots as a stand-alone device.
The device units are shipped with the default Unit ID of the stand-alone unit. If the device is operating as a stand-
alone unit, all stacking LEDs are off. Once the user selects a different Unit ID, the default Unit ID not erased, and
remains valid, even if the unit is reset.
Unit ID 1 and Unit ID 2 are reserved for Master enabled units. Unit IDs 3 to 6 can be defined for stack members.
When the Master unit boots or when inserting or removing a stack member, the Master unit initiates a stacking dis-
covering process.
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