Service Manual

Stack Master Election
The stack elects a master and standby unit at bootup time based on two criteria.
• Unit priority — User-congurable. The range is from 1 to 14. A higher value (14) means a higher priority. The default is 1. By
removing the stack-unit priority using the
no stack-unit priority command, you can set the priority back to the default
value of zero. The unit with the highest priority is elected the master management unit; the unit with the second highest priority
is elected the standby unit.
• MAC address (in case of priority tie) — The unit with the higher MAC value becomes the master unit. The stack takes the
MAC address of the master unit and retains it unless it is reloaded.
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 and all the units come up at the same time; for example, when all units boot up from ash, all units participate
in the election and the master and standby are chosen based on the priority or MAC address.
When the units do not boot up at the same time, such as when some units are powered down just after reloading and powered up
later to join the stack, they do not participate in the election process even though the units that boot up late may have a higher
priority congured. This happens because the master and standby have already been elected, hence the unit that boots up late joins
only as a member.
When an up and running standalone unit or stack is merged with another stack, based on election, the losing stack reloads and the
master unit of the winning stack becomes the master of the merged stack. For more details, see sections Add Units to an Existing S-
Series Stack and Remove Units or Front End Ports from a Stack. It is possible to reset individual units to force them to give up the
management role or reload the whole stack from the CLI to ensure a fully synchronized bootup.
Example of Viewing Stack Members
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 congure a virtual IP: Dell(conf)#virtual-ip {ip-address | ipv6–address |
dhcp}
Failover Roles
If the stack master fails (for example, is powered o), 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.
To view failover details, use the show redundancy command.
Stacking
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