Hitless Stacking Overview

Hitless stacking is supported on FastIron units in a stack. It is a High Availability feature set that provides sub-second convergence during the following events:

  • Stack failover
  • Stack switchover
  • Stack trunk failover
  • Stack topology changes

During such events, the standby controller takes over the active role, and the system continues to forward traffic seamlessly as if no failure had 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.

Note: The traffic that does not pass through the failed active controller is hitless when any of these events occur. When a ring stack transitions to a linear stack, however, the traffic interruption remains in the 1-3 second range for traffic that needs to be rerouted.

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 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 may be caused by 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.

Parent topic: Hitless Stacking