178 Managing a Switch Stack
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 359.
What is Stacking Standby?
A standby unit is preconfigured in the stack. If the current stack master fails,
the standby unit becomes the stack master. 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 stack master has already been elected.
The stack master 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 stack master becomes unavailable.
Operational state synchronization also occurs:
• when you save the running configuration to the startup configuration on
the stack master.
• when the backup unit changes.
What is Nonstop Forwarding?
Networking devices, such as the Dell Networking 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 stack master acts as the control
plane. The management plane is application software running on the stack
master that provides interfaces allowing a network administrator to configure
the device.
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
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