How is the Firmware Updated on the Stack?
When you add a new switch to a stack, the Stack Firmware Synchronization
feature automatically synchronizes the firmware version with the version
running on the stack master. The synchronization operation may result in
either upgrade or downgrade of firmware on the mismatched stack member.
Upgrading the firmware on a stack of switches is the same as upgrading the
firmware on a single switch. After you download a new image by using the File
Download page or copy command, the downloaded image is distributed to all
the connected units of the stack. For more information about downloading
and installing images, see "Managing Images and Files" on page 363.
What is Stacking Standby?
A Standby unit is preconfigured in the stack. If the current Master unit fails,
the Standby unit becomes the Master unit. If no switch is pre-configured as
the Standby unit, the software automatically selects a Standby unit from the
existing stack units.
When the failed Master resumes normal operation, it joins the stack as a
member (not a Master) if the new Master unit has already been elected.
The Master unit copies its running configuration to the Standby unit
whenever it changes (subject to some restrictions to reduce overhead). This
enables the Standby unit to take over the stack operation with minimal
interruption if the Master unit becomes unavailable.
The running-config synchronization also occurs:
when you save the running configuration to the startup configuration on
the Master unit.
when the backup unit changes.
What is Nonstop Forwarding?
Networking devices are often described in terms of three semi-independent
functions called the forwarding plane, the control plane, and the
management plane. The forwarding plane forwards data packets and is
implemented in hardware. The control plane is the set of protocols that
determine how the forwarding plane should forward packets, deciding which
data packets are allowed to be forwarded and where they should go.
Application software on the Management Unit acts as the control plane. The
Managing a Switch Stack