User Manual

M4300 Intelligent Edge Series Fully Managed Stackable Switches
Manage Stacking User Manual166
preference can be assigned by the administrator. However, if all units are assigned the
same management preference, then the unit with the highest MAC address is assigned
as the stack master.
Stack Factory Defaults Reset Behavior
If the stack master is reset to the factory default settings (see Reset the Switch to Its Factory
Default Settings on page 672), the stack master applies the default settings to all the stack
members and resets the stack, including all participating stack members. When the stack
boots, the stack master election process begins.
A switch can be 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. The forwarding plane is implemented in hardware. The control plane is the set of
protocols that determine how the forwarding plane forwards packets, deciding which data
packets are allowed to be forwarded and where they go. Application software on the
management unit acts as the control plane. The management plane is application software
running on the management unit that provides interfaces allowing a network administrator to
configure and monitor the device.
Stack NSF
Nonstop forwarding (NSF) 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. A nonstop forwarding failover can
also be manually initiated by clicking the Initiate Failover button on the NSF Summary page.
Traffic flows that enter and exit the stack through physical ports on a unit other than the
management continue with at most sub-second interruption when the management unit fails.
To prepare the backup management unit in case of a failover, applications on the
management unit continuously checkpoint some state information to the backup unit.
Changes to the running configuration are automatically copied to the backup unit. 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 backup unit starts from a
partially initialized state and applies the checkpointed state information. While the control
plane is initializing, the stack cannot react to external changes, such as network topology
changes. Once the control plane is fully operational on the new management unit, the control
plane ensures that the hardware state is updated as necessary
. Control plane failover time
depends on the size of the stack, the complexity of the configuration, and the speed of the
CPU.
The management plane restarts when a failover occurs. Management connections must be
reestablished.