Hitless stacking overview

Hitless stacking is supported on FastIron units in a traditional stack. It is a High Availability feature set that ensures sub-second or no loss of data traffic during the following events:

• Active controller failure or role change
• Software failure
• Addition or removal of units in a stack
• Removal or disconnection of the stacking cable between the active controller and the standby controller

During such events, the standby controller takes over the active role, and the system continues to forward traffic seamlessly, as if no failure or topology change has occurred. In software releases that do not support hitless stacking, events such as these could cause most of the units in a stack to reset, affecting data traffic.

FastIron stackable units support the following hitless stacking features:

Hitless stacking switchover - A manually-controlled (CLI-driven) or automatic switchover of the active controller and standby controller without reloading the stack and without any packet loss to the services and protocols that are supported by hitless stacking. A switchover is activated by the CLI command stack switch-over command. A switchover may also be activated by the priority command, depending on the configured priority value.

Hitless stacking failover - An automatic, forced switchover of the active controller and standby controller because of a failure or abnormal termination of the active controller. During a failover, the active controller abruptly leaves the stack, and the standby controller immediately assumes the active role. As with a switchover, a failover occurs without the stack being reloaded. Unlike a switchover, a failover generally occurs without warning and is likely to result in sub-second packet loss (although packets traversing the stacking link may be lost).

Hitless stacking failover is enabled by default beginning with Fastiron release 08.0.20.