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 tojoin 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 masterunit of the winning stack becomes the master of the merged stack. For more details, see sectionsAdd Units to an Existing Stack andRemove a Unit from a Stack. It is possible to reset individual units to force them to give up the management role or reload the whole stackfrom the CLI to ensure a fully synchronized bootup.Example of Viewing Stack MembersVirtual IPYou 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 RolesIf 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 standbyrole to the master role. The distributed forwarding tables are retained during the failover, as is the stack MAC address. The lack of astandby 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 insteadtakes the next available role.To view failover details, use the show redundancy command.MAC Addressing on StacksThe stack has three MAC addresses: the chassis MAC, interface MAC, and null interface MAC.All interfaces in the stack use the interface MAC address of the management unit, and the chassis MAC for the stack is the master’schassis MAC. The stack continues to use the master’s chassis MAC address even after a failover. The MAC address is not refreshed untilthe stack is reloaded and a different unit becomes the stack master.NOTE: If the removed management unit is brought up as a standalone unit or as part of a different stack, there is a possibility ofMAC address collisions.A standalone is added to a stack. The standalone and the master unit have the same priority, but the standalone has a lower MAC address,so the standalone reboots. In the second example, a standalone is added to a stack. The standalone has a higher priority than the stack, sothe stack (excluding the new unit) reloads.Example of Adding a Standalone with a Lower MAC Address to a Stack----------STANDALONE BEFORE CONNECTION---------------Standalone#show system briefStack MAC : 00:01:e8:d5:ef:81-- Stack Info --Unit UnitType Status ReqTyp CurTyp Version Ports------------------------------------------------------0 Management online898 Stacking
