NETGEAR M4350-24F4V 24-Port 10G SFP+ Managed AV Network Switch - Manual (Page 55)

Stack nonstop forwarding
Nonstop forwarding (NSF) allows the forwarding plane of stack members 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 switch. If the
management switch fails, traffic flows can continue to enter and exit the stack through
physical ports on any member other than the management switch with less than one
second of interruption.
You can also initiate a nonstop forwarding failover to a standby management switch
(see Configure nonstop forwarding and display associated information on page 56).
To prepare the standby management switch, applications on the management switch
continuously forward information to the standby unit. Changes to the running
configuration are automatically copied to the standby management switch. MAC
addresses stay the same across a nonstop forwarding failover so that neighbors are not
required to relearn them.
When a nonstop forwarding failover occurs, the control plane on the standby
management switch applies the information that it received from the management
switch. When the control plane is initializing, the stack cannot react to external changes,
such as network topology changes. After the control plane is fully operational on the
new management switch (which was previously the standby management switch), the
control plane updates hardware changes as needed. Control plane failover time depends
on the size of the stack, the complexity of the configuration, and the speed of the switch
CPU.
The management plane restarts when a failover occurs. Management connections must
be reestablished.
For NSF to be effective, adjacent networking devices must not reroute traffic around
the restarting device. The switch uses three techniques to prevent traffic from being
rerouted:
• A protocol can distribute a part of its control plane to stack members so that the
protocol can give the appearance that it is still functional during the restart. Spanning
tree and port channels use this technique.
• A protocol can enlist the cooperation of its neighbors through a technique known
as graceful restart. OSPF uses graceful restart if it is enabled.
• A protocol can restart after the failover if neighbors react slowly enough that they
cannot detect the outage. The IP multicast routing protocols are a good example of
this behavior.
To take full advantage of nonstop forwarding, Layer 2 connections to neighbors must
be through port channels that span two or more stack members, and Layer 3 routes
must be equal-cost multipath (ECMP) routes with next hops through physical ports on
Main User Manual 55 Manage Stacking
Fully Managed Switches M4350 Series Main User Manual