Configuration Guide User guide

FastIron Configuration Guide 327
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More about IronStack technology
If the Active Controller fails, the Standby Controller waits 30 seconds, and then takes over as Active
Controller, resetting itself and all other stack members. If the old Active Controller becomes
operational, it may or may not resume its role as Active, depending on the configured priorities. If
hitless stacking failover is enabled, the standby unit can take over immediately without reloading
any unit.
Standby Controller
In addition to the Active Controller, another stack member is elected as the Standby Controller.
After a default interval of 30 seconds, the Standby Controller takes over if the Active Controller
fails. If hitless stacking failover is enabled, the standby unit can take over immediately without
reloading any unit.
NOTE
Because it can take as long as 20 seconds to age out a neighbor, the Standby takeover period may
last up to 50 seconds. Refer to “Port down and aging” on page 326.
The Standby Controller synchronizes its configuration with the Active Controller at each reset.
Bootup role
When a stack unit boots, it boots in a particular role, such as standalone, Active Controller, Standby
Controller, or stack member. When the bootup role is Standby Controller or stack member, the CLI
available to the unit is limited to show and stack commands. A unit in the role of Standby or stack
member will not act without instructions from the Active Controller. To convert a Standby Controller
or stack member into a standalone device, use the stack unconfigure me command (refer to
“Unconfiguring an IronStack” on page 287).
The last line of the show version output identifies the unit role unless the unit is in standalone
mode.
Example
My stack unit ID = 1, bootup role = active
My stack unit ID = 3, bootup role = standby
Active Controller and Standby Controller elections
Whenever there is a topology change in the stack (a reset, unit failure, or the addition or removal of
members), elections are held to determine the status of the Active Controller and Standby
Controller. The results of the election take effect after the next stack reset.
The following conditions, in the order shown, determine which units will serve as Active Controller
and Standby Controller after an election:
• Boot as Active Controller - Indicates that a unit was previously Active Controller before the
current boot sequence and will again assume the role of Active Controller when two standalone
units are combined into a stack. When a third standalone unit joins the stack, a current Active
Controller becomes subject to the other factors in this list. The reason for this hierarchy of
factors is to achieve a predictable winner regardless of the boot up sequence for a unit. You
can upgrade your current Active Controller to “boot as active controller” status by performing a
write memory. The system interprets the write memory action as a directive to maintain the
current Active Controller role regardless of resets or a new unit joining the stack.
• Priority - The unit with the highest priority value.