White Papers

Master Selection Criteria
A Master is elected or re-elected based on the following considerations, in order:
1. The switch with the highest priority at boot time.
2. The switch with the highest MAC address at boot time.
3. A unit is selected as Standby by the administrator, and a fail over action is manually initiated or occurs due to a Master unit
failure.
No record of previous stack mastership is kept when a stack loses power. As it reboots, the election process will once again
determine the Master and Standby switches. As long as the priority has not changed on any members, the stack will retain the
same Master and Standby.
NOTE: Each stack members’ role (including the Master and Standby) can be defined by the user at any time by setting the
priority.
If the entire stack is powered OFF and ON again, the unit that was the Master before the reboot will remain the Master after
the stack resumes operation. However, when a stack is powered on, all members are in sleep mode for 5 seconds while waiting
on the previous Master to join the stack. If the previous Master fails to join within 5 seconds, the remaining members (including
the Standby) elect a new Master.
Configuring Priority and stack-group
Perform the following steps to configure the priorities and stack-groups for each of the switches.
1. Set the priorities for the stack-unit.
CONFIGURATION mode
stack-unit unit-number priority 1-14
Dell(conf)# stack-unit 0 priority 12
Setting the priority will determine which switch will become the management (Master) switch. The switch with the highest
priority number is elected Master. The default priority is 0.
NOTE:
It is best practice to assign priority values to all switches before stacking them in order to acquire and retain
complete control over each units role in the stack.
2. Configure the stack-group for each stack-unit.
CONFIGURATION mode
stack-unit unit-no stack-group stack-group-id
Dell(conf)# stack-unit 0 stack-group 0
Dell (conf)#02:26:05: %STKUNIT0-M:CP %IFMGR-6-STACK_PORTS_ADDED:
Ports Fo 0/33 have been configured as stacking ports.
Please save and reload for config to take effect
Stack-groups are easier to think of simply as stack ports. For example, using the stack-group 0 command simply
turns the lower port (port 9) into a stacking port. Similarly, stack-group 1, stack-group 2 and stack-group 3
commands correspond to ports 10, 11 and 12 respectively.
NOTE: Stack-group is supported only in PMUX mode.
3. Continue to run the stack-unit 0 stack-group <0-3> command to add additional stack ports to the switch, using
the stack-group mapping.
Cabling the Switch Stack
Dell PowerEdge FN I/O Aggregators are connected to operate as a single stack in a ring topology using the SFP+ or Base-T
ports on the front end ports 9 and 10. To create a stack in either a ring or daisy-chain topology, you can use two units on the
same chassis or up to six units across multiple chassis.
Prerequisite: Before you attach the stacking cables, all Aggregators in the stack must be powered up with the default or
reconfigured settings.
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Stacking