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DGS-3100 Series Gigabit Stackable Managed Switch User Manual
17
Electing a Stacking Master
Whenever a stacking member (or more than one) comes up, one of the stacking members is elected to be the stack Master.
The Stack Master is selected as follows:
• If one of the master enabled stacking members in the stack was set to Force Master by the system administrator
(through the GUI – Stacking Master selector), that master enabled stacking member is the Stack Master. Stacking
members which are defined as Force Master stacking members are manually selected as the Stack Master. Only a
master enabled stacking member can be selected as the Force Master.
• If the stack contains more than one stacking member whose Unit ID is either 1 or 2, then one of the stacking
members are elected the Stack Master. It does not matter if the Unit ID was originally automatically or manually
assigned. These stacking members are called Master Enabled. If there is only one stacking member, that stacking
member is selected as the Stack Master, even if the stacking member’s Unit ID is 2.
• If there are more than one stacking members, the two stacking members decide which stacking member is elected
Stack Master by checking:
– Which stacking member has been running for a longer time. The up-time is measured in increments of 10
minutes. The stacking member running the longest is elected the Stack Master.
– If they have been running for the same amount of time, the stacking member with the Unit ID 1 is the stack
Master.
– If both stacking members have been running for the same amount of time, and both stacking membes have the
same Unit ID, the stacking members with the lowest MAC addressis selected as the Stack Master. The other
unit is rebooted and is assigned the Unit ID 2.
– If the stack contains one or more stacking members set to the factory default states, and there is no Unit ID
assigned to a stacking member, then the Stack Master is one of these stacking members. The stacking member
selected to be the Master is the stacking member running for the longest time. If all stacking members are
running the same amount of time, the stacking member with the lowest MAC address is selected as the Stack
Master.
The Master Election results in an elected Stack Master. The Stack master has a Unit ID of 1 and the Backup Master has a
Unit ID of 2 (if a Backup Master was included in the stack).
If a Master Enabled stacking member, a Unit ID of 1 or 2, is added to a stack and powered on, the newly added switch
invokes Master Election process. The Master Election process occurs even though the stack has an elected master. However,
the newly added switch loses in the election process (lower up-time) and joins the stack as a stacking member or Backup
Master.
Stack Startup Process
When a stacking member is initialized, either powered up or rebooted, the stacking member goes through the same exact
process including:
•
Discovering the Stacking Master.
•
Allocating Unit IDs/Resolving Unit ID Conflicts
•
Unit and Stacking Port Configuration
Discovering the Stacking Master
When a stacking member is initialized in stack mode, the stacking member’s behavior depends on its Unit ID.
• If the stacking member does not have a current Unit ID the stacking member operates in Factory Default mode. If
there is a Stacking Master, the stacking member is assigned a Unit ID through Unit ID Allocation. The stacking
members receive a Unit ID from the Stacking Master. If the stack does not have a Stacking master then the switch
participates in Master-Election, and may be elected either the new Stacking Master or Backup Master.
• If the stacking member’s current Unit ID is 1 or 2, the stacking member participates in the Master Election. For
example, the Unit ID was previously allocated, or the stacking member was in a different stack.
• If the stacking member has a current Unit ID the stacking members attempts to use the Unit ID in the new stack. If
the stacking member current ID is 3, 4, 5, or 6, then the stacking members attempts to connect to the running Stack
Master. The new stacking member does not proceed to the next stage until there is contact with the Stack Master.