White Papers

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
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.
Use the following command to configure a virtual IP: Dell(conf)#virtual-ip {ip-address | ipv6–address |
dhcp}
Failover Roles
If the stack master fails (for example, is 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 the
standby role to the master role. The distributed forwarding tables are retained during the failover, as is the stack MAC address.
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 takes the next available role.
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Stacking