Service Manual

Stack Master Election
The stack elects a master and standby unit at bootup time based on two criteria.
• Unit priority — User-configurable. 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 offline.
• 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 flash, 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 configured. 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 sectionsAdd Units to an Existing 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 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
Stacking
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