C
ONNECTING
S
WITCHES
IN
A
S
TACK
3-9
5. Select the Master unit in the stack by pressing the push button in on
only one of the switches. Only one switch in the stack can operate as
the Master, all other units operate in slave mode. If more than one
switch in the stack is selected as Master, or if no switches are selected,
the system will select the unit with lowest MAC address as the Master.
Stacking Topologies
All units in the stack must be connected via stacking cable. You can
connect units in a simple cascade configuration, connecting Up ports to
Down ports, from the top unit to the bottom unit. Using this “line”
topology, if any link or unit in the stack fails, the stack is split and two
separate segments are formed. The Stack Link LEDs on the units th at are
disconnected flash to indicate that the stack link between them is not
functioning (see Table 1-2 “System Status LEDs” on page 1-6).
When a stack link failure occurs, the stack reboots and a Master unit is
selected within each of the two stack segments. The Master unit will be
either the unit with the Master button depressed or the unit with the
lowest MAC address if the Master button is not depressed on any unit.
When the stack reboots and resumes operations, note that the IP address
will be the same for both of the stack segments. To resolve the conflicting
IP addresses, you should manually replace the failed link or unit as soon as
possible. If you are using a wrap-around stack topology, a single point of
failure in the stack will not cause the stack to fail. It would take two or
more points of failure to split the stack.
If the Master unit fails or is powered off, the backup unit will take control
of the stack without any loss of configuration settings. The Slave unit with
the lowest MAC address is selected as the backup unit.