- 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 syst em will s elec t
the unit with the lowest MAC addre ss as the stac k Maste r.
• When the stack is initially powered o n, t he 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 switc h. It can als o be
selected on the front panel graphic of the web interfac e, or from the CLI.
• If the Master unit fails and another unit takes over control of th e stack, th e unit
numbering will not change.
• If a unit in the stack fails or is removed from the stack, the unit numbers w ill not
change. This means that when you replace a uni t in the st ack, the orig inal
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 un it, 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, plac e the Slav e unit with the lowe st
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 i s
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, a nd
then select another backup unit after the stack finishes reboot ing. Also n ote 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 th e s tack (due to a po wer dow n or failure ) or a new
unit added to the stack, the original unit IDs are not affected after rebo oting, and a
new unit is assigned the lowest availabl e unit I D.

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 configurat ion from the top to the bot tom uni t. Us ing 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