Users Guide

262 Stacking
The management unit in the stack 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 management unit in the stack becomes
unavailable.
Operational state synchronization also occurs:
• when the running configuration is saved to the startup configuration on
the management unit in the stack .
• when the standby unit changes.
What is Nonstop Forwarding?
Networking devices, such as the Dell EMC Networking N-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
management unit in the stack acts as the control plane. The management
plane is application software running on the management unit in the stack
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
on the management unit in the stack. This type of operation is called nonstop
forwarding (NSF). When the management unit in the stack fails, only the
switch ASICs and processor on the management unit in the stack need to be
restarted.
To prevent adjacent networking devices from rerouting traffic around the
restarting device, the NSF feature uses the following three techniques:
1 A protocol can distribute a part of its control plane across stack units so
that the protocol can give the appearance that it is still functional during
the restart.
2 A protocol may enlist the cooperation of its neighbors through a technique
known as graceful restart.