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6.5 Powering Considerations
Stack members that are powered on within the same 20-second time frame participate in the stack
master election and have a chance to become the stack master. If the stack members that are powered
on after the 20-second time frame do not participate in this initial election and a re-election process will
be issued, all of the stack members must participate in the re-election process.
The new stack master becomes available after a few seconds. In the meantime, the switch stack uses
the forwarding tables in memory to minimize network disruption.
Consider the following guidelines before you turn on the switches in a stack. The purpose of the
guidelines is to prevent the stack master is changed as you add new switches into the stack system. If
the stack master is changed, the traffic might be interrupted and the configuration might be lost. (See
Master Election Process section) For the first time installation, we recommend you to set the highest
priority for a switch if this switch will be the stack master in your stack system.
1. The sequence in which you initially turn on the switch might affect the switch that becomes the
master of the stack.
2. If you want a particular switch to become the stack master turn on that switch first. This switch
becomes the stack master and remains the stack master until a master re-election is required.
After about 20 seconds, power on the remaining switches in the stack.
3. Switch that you add to an existing stack has to be connected to the stack via stacking cable
within next 20 seconds after it is powered on.
4. Adding powered-on switches (merging) causes the stack masters of the merging switch stacks to
re-elect a new stack master from among themselves. All remaining switches will be reconfigured
by the new stack master. If the stack master is not the original one, the traffic will be interrupted
during the reconfiguration.
5. Removing the stack master will cause the standby switch to take over the master role. All
remaining switches will be reconfigured by the new stack master. The traffic will be interrupted
during the reconfiguration.
6. Removing stack members from a non-ring topology will cause the switch stack to be divided
(partition) into two or more switch stacks; each of them will have the same configuration. This
can cause an IP address configuration conflict in your network. If you want the switch stacks to
remain to separate, change the IP address or addresses of the newly created switch stacks. If
you did not intend to partition the switch stack:
a) Power off the switches in the newly created switch stacks.
b) Reconnect them to the original switch stack through their stacking ports.
c) Power them on again.
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