White Papers

Stacking and VLT
Dell EMC Technical White Paper
2.5 Removal of the switch from the stack
Before removing any member from the stack ensure that the other members of the stack will not become
isolated from the stack due to the removal. Also, ensure that the ring topology can form a communication path
around the member must be removed.
Note that when removing a switch from the stack, disconnect all the links on the stack member. Also, statically
re-route any traffic going through this unit. When a unit in a stack fails, the stack master removes the failed unit
from the stack. The failed unit reboots with its original running-configuration. If the stack is configured in a ring
topology, then the master stack automatically re-routes the traffic around the failed unit. If the stack is not
configured in ring topology, the stack may split and the isolated units will then reboot and re-elect a new stack
master. If a switch is removed and you plan to renumber the stack, issue a no-member unit command in stack
configuration mode to delete the removed switch from the configured stack information.
2.6 Stacking standby
The standby unit may be pre-configured or automatically selected. If the stack master fails, the standby unit
becomes the new stack master. If there is no switch in the stack that is configured as a standby unit, the software
automatically selects a standby unit from among the existing stack. When the failed master switch resumes
normal operation, it joins the stack as a member if the new stack master has already been elected. If the new
stack master fails, the member unit then takes over as the master switch.
2.7 Failover roles
If the stack master fails or it is powered off, it is removed from stack topology.
The standby unit detects the loss of peering communication and takes ownership of stack management,
switching itself from the standby role to the master role. The distrusted forwarding tables are retained during
the failover, as is the stack MAC address. The lack of a standby unit triggers an election within the remaining
units for a standby role.
After the former master switch recovers, despite having a higher priority or MAC address, it does not recover
its master role but instead takes the next available role. View further details through show redundancy
command.
2.8 Creating a stack
The stack elects a master and standby unit at bootup based on the Unit Priority or MAC Address. The unit
priority is user configurable. The available range is from 1 – 14, with a higher value indicating a higher priority.
By using the no stack-unit priority command, the priority can be set back to zero. The unit that is higher in
priority is selected as the master unit and the unit that is lower in priority is set as the standby unit.
In case the priority is same on both master and standby unit, the unit with the higher MAC value becomes the
master unit. The stack takes the MAC address of the master unit and retains it unless it is reloaded.
The device supports stacking in a ring or a daisy chain topology. Dell Networking recommends the ring topology
when stacking the switches to provide redundant connectivity.