140 Managing a Switch Stack
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 349.
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, such as the PowerConnect 7000 Series switches, 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