Reference Guide

854 | Stacking
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• 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.
For more information, refer to Adding a Stack Unit and Removing a Switch from a Stack.
Figure 48-2. Displaying the Stack Master
Failover Roles
If the stack master fails (for example, powered off), it is removed from the stack topology. The standby unit
detects the loss of peering communication and takes ownership of the stack management, switching from
standby to master. The lack of a standby unit triggers an election within the remaining units for a standby
role.
After the former master switch recovers, despite having a higher priority or MAC address, it does not
recover its master role but instead take the next available role.
MAC Addressing
All port interfaces in the stack use the MAC address of the management interface on the master switch.
The MAC address of the chassis in which the master S5000 switch is installed is used as the stack MAC
address.
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
9 Member not present
10 Member not present
11 Member not present