Brocade FastIron Ethernet Switch Stacking Configuration Guide - Manual (Page 99)

• Addition or removal of units in a stack
• Removal or disconnection of the stacking cable between the active and standby controllers
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,
resulting in an impact to data traffic.
The following hitless stacking features are supported:
Hitless stacking switchover - A manually-controlled (CLI-driven) or automatic switchover of the active
and standby controllers 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. A switchover might also be activated by the CLI command priority, depending on the
configured priority value.
Hitless stacking failover - An automatic, forced switchover of the active and standby controllers
because of a failure or abnormal termination of the active controller. In the event of a failover, the active
controller abruptly leaves the stack and the standby controller immediately assumes the active role. Like
a switchover, a failover occurs without reloading the stack. Unlike a switchover, a failover generally
happens without warning and will likely have sub-second packet loss (packets traversing the stacking
link may be lost) for a brief period of time.
Hitless stacking is disabled by default.
Supported hitless stacking events
The following events are supported by hitless stacking:
• Failover
• Switchover
• Priority change
• Role change
Non-supported hitless stacking events
The following events are not supported by hitless stacking. These events require a software reload,
resulting in an impact to data traffic.
• Unit ID change - When a stack is formed or when a unit is renumbered using secure-setup.
• Stack merge - When the old active controller comes back up, it reboots. If it has fewer number of
members than the active controller, it loses the election, regardless of its priority. If it has a higher
priority, it becomes the standby controller after the reboot and is synchronized with the active
controller. Next, a switchover occurs and it becomes the new active controller.
Supported hitless stacking protocols and services
The following table highlights the impact of a hitless switchover or failover to the major functions of the
system.
NOTE
Services and protocols that are not listed in the following table will encounter disruptions, but will
resume normal operation once the new active controller is back up and running.
Supported hitless stacking events
FastIron Ethernet Switch Stacking Configuration Guide 97
53-1003090-02