Reference Guide

Stack Master Election
By default, the stack determines a master and standby unit at bootup time by electing the units with the
highest MAC addresses.
You can preconfigure the units which are elected master and standby by assigning higher priorities to
these units. (By default, all stack units have priority 0. Valid priority values are from 0 to 14. A higher value
means a higher priority. To remove the stack-unit priority and set the priority back to the default value of
zero, use the no stack-unit priority command.)
If you add a standalone unit, which has the same priority as the master stack unit, the standalone unit
joins the stack as a member unit.
NOTE: The units with the highest MAC addresses become master and standby only if you do not
configure priorities. The MAC address of the master unit is refreshed only when the stack is reloaded
and a different unit becomes the stack manager.
To view which switch is the stack master, enter the show system command. The following example
shows sample output from an established stack.
A change in the stack master occurs when:
• You power down the stack master or bring the master switch offline.
• A failover of the master switch occurs.
• You disconnect the master switch from the stack.
When a stack reloads, the stack master is determined as follows:
• When a stack reloads and all units come up at the same time (for example, when all units boot up
from flash), all units participate in the election. The master and standby are chosen based on the
highest MAC address or (if configured) the highest priorities.
• When stack units do not boot up at the same time (for example, some units are powered down just
after reloading and powered up later to join the stack), the units that boot up later do not participate
in the election process, even though these units may have a higher priority configured. This happens
because the master and standby have already been elected; therefore, the unit that boots up late joins
only as a member. To include late-booting units in the master election, reload the stack.
• When a stack or standalone unit that is up and running is merged with another stack, according to the
master election, the losing stack reloads and the master unit of the winning stack becomes the master
of the merged stack.
Example of Viewing Stack Members
S5000-1#show system brief
Stack MAC : 5c:f9:dd:ef:06:00
Reload-Type : normal-reload [Next boot : normal-reload]
-- Stack Info --
Unit UnitType Status ReqTyp CurTyp Version
--------------------------------------------------
0 Member not present S5000
1 Standby online S5000 S5000 9-0-1-0
2 Management online S5000 S5000 9-0-1-0
3 Member not present S5000
4 Member not present S5000
5 Member not present
6 Member not present
7 Member not present
8 Member not present
902
Stacking