White Papers

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 precongure 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 congure priorities. The MAC
address of the master unit is refreshed only when the stack is reloaded and a dierent 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 oine.
• 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 ash), all units participate in the
election. The master and standby are chosen based on the highest MAC address or (if congured) 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 congured. 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
9 Member not present
10 Member not present
11 Member not present
Virtual IP
You can manage the stack using a single IP, known as a virtual IP, that is retained in the stack even after a failover.
The virtual IP address is used to log in to the current master unit of the stack. Both IPv4 and IPv6 addresses are supported as virtual IPs.
Stacking
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