62 Switch Feature Overview
Master Failover with Transparent Transition
The stacking feature supports a

standby

or backup unit that assumes the
stack master role if the stack master fails. As soon as a stack master failure is
detected, the standby unit initializes the control plane and enables all other
stack units with the current configuration. The standby unit maintains a
synchronized copy of the running configuration for the stack.
Nonstop Forwarding on the Stack
The Nonstop Forwarding (NSF) feature allows the forwarding plane of stack
units to continue to forward packets while the control and management
planes restart as a result of a power failure, hardware failure, or software fault
on the stack master and allows the standby switch to quickly takeover as the
master.
Hot Add/Delete and Firmware Synchronization
You can add and remove units to and from the stack without cycling the
power. When you add a unit, the Stack Firmware Synchronization feature, if
enabled, automatically synchronizes the firmware version with the version
running on the stack master. The synchronization operation may result in
either an upgrade or a downgrade of firmware on the mismatched stack
member. Once the firmware is synchronized on a member unit, the running-
config on the member is updated to match the master switch. The startup-
config on the standby and member switches is not updated to match the
master switch due to configuration changes on the master switch. Saving the
startup config on the master switch also saves it to the startup config on all
the other stack members.The hardware configuration of every switch is
updated to match the master switch (unit number, slot configuration, stack
member number, etc.).