Users Guide

Switch Feature Overview 65
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
Units can be added to and deleted from the stack without cycling the power
on the stack. Units to be added to the stack must be powered off prior to
cabling into the stack to avoid election of a new master unit and a possible
downgrade of the stack. When the newly added unit is powered on, 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.).
NOTE: ALWAYS POWER OFF a unit to be added to a stack prior to cabling it into
the stack. Newly added units must be powered on one-at-a-time beginning with
the unit directly connected to an already powered on stack member.