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- If Master/Slave push button is depressed on more than one unit, the system will
select the unit with the lowest MAC address from those with the push button
depressed as the stack Master.
- If Master/Slave push button is not depressed on any unit, the system will select
the unit with the lowest MAC address as the stack Master.
• When the stack is initially powered on, the Master unit is designated as unit 1 for a
ring topology. For a line topology, the stack is simply numbered from top to bottom,
with the first unit in the stack designated at unit 1. This unit identification number
appears on the Stack Unit ID LED on the front panel of the switch. It can also be
selected on the front panel graphic of the web interface, or from the CLI.
• If the Master unit fails and another unit takes over control of the stack, the unit
numbering will not change.
• If a unit in the stack fails or is removed from the stack, the unit numbers will not
change. This means that when you replace a unit in the stack, the original
configuration for the failed unit will be restored to the replacement unit.
• If a unit is removed from the stack and later reattached to the stack, it will retain the
original unit number obtained during stacking.
• If a unit is removed from the stack, and powered up as a stand-alone unit, it will
also retain the original unit number obtained during stacking.
Selecting the Backup Unit
Once the Master unit finishes booting up, it continues to synchronize configuration
information to all of the Slave units in the stack. If the Master unit fails or is powered
off, a new master unit will be selected based on the election rules described in the
preceding section. The backup unit elected to serve as the new stack Master will
take control of the stack without any loss of configuration settings. To ensure a
logical fail over to next unit down in the stack, place the Slave unit with the lowest
MAC address directly beneath the Master unit in the stack.
Recovering from Stack Failure or Topology Change
When a link or unit in the stack fails, a trap message is sent and a failure event is
logged. The stack will be rebooted after any system failure or topology change. It
takes two to three minutes to for the stack to reboot. If the Master unit fails, the
backup unit will take over operations as the new Master unit, reboot the stack, and
then select another backup unit after the stack finishes rebooting. Also note that
powering down a unit or inserting a new unit in the stack will cause the stack to
reboot. If a unit is removed from the stack (due to a power down or failure) or a new
unit added to the stack, the original unit IDs are not affected after rebooting, and a
new unit is assigned the lowest available unit ID.
Broken Link for Line and Wrap-around Topologies
All units in the stack must be connected via stacking cable. You can connect the
units in a simple cascade configuration from the top to the bottom unit. Using this
kind of line topology, if any link or unit in the stack fails, the stack will be broken in
2-4
Initial Configuration
2