Quick Reference Guide

86 | Stacking S-Series Switches
www.dell.com | support.dell.com
to be a management unit, then the newly added unit changes its configured value to disable the
management unit function.
• Conversely, if the management unit function is enabled or unassigned on the unit and there is no other
management unit in the system, then the unit becomes the management unit.
• If the management unit function is disabled on the unit, then it remains a non-management unit.
• The priority preference (
switch priority command) is only used to select the next management unit
when the current management unit fails.
• When two units that constitute the members of a stack come up at the same time, then whichever has
the higher priority or higher MAC address becomes the management unit.
• The current management unit has the highest default preference for staying the manager after a reboot.
On reboot, a member switch waits for 30 seconds to hear from the management unit before it begins to
determine from its priority if it must become the management unit. Therefore, in addition to the
movemanagement command cited above, you could force a change in management units in this way:
1. Power down the current management unit.
2. Reset the stack. Enter the
reload command.
3. Wait more than 30 seconds before powering up the device again.
At 30 seconds, the remaining units start the management unit election process.
Unit Number Assignment
You can manually assign numbers to stack members. For details, see Adding a Switch to a Stack on
page 89. Otherwise, SFTOS automatically assigns unit numbers based on the following factors.
• If the unit number is configured, but another unit already uses that number, the unit changes its
configured unit number to the lowest unassigned unit number.
• If the unit number is unassigned, then the unit sets its configured unit number to the lowest unassigned
unit number.
• If the unit number is configured and no other device uses the unit number, then the unit starts using the
configured unit number.
• If a unit detects that the maximum number of units already exist, the unit sets its unit number to
“unassigned” and stays in the Initialization state.
Stack Management and Functionality
As described above (Management Unit Selection Algorithm on page 85), a management selection
algorithm elects one stack member to be the management unit. All other switches in the stack will be
subordinate to the management unit and “assume its personality”. Each switch in the stack will have a unit
number that you can configure, or they are set automatically by the individual units as they start (Unit