Netgear GS728TP Manual do Utilizador descarregar pdf (Página 71)

Configuring System Information

ProSafe M5300 Switch

Nonstop Forwarding

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 do not have

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.

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:

1. A protocol may distribute a part of its control plane to stack units so that the protocol can

give the appearance that it is still functional during the restart. Spanning tree and port

channels use this technique.

2. A protocol may enlist the cooperation of its neighbors through a technique known as

graceful restart. OSPF uses graceful restart if it is enabled.

3. A protocol may simply restart after the failover if neighbors react slowly enough that they will

not normally 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 should be via

port channels that span two or more stack units, and layer 3 routes should be ECMP routes

with next hops via physical ports on two or more units. The hardware can quickly move traffic

flows from port channel members or ECMP paths on a failed unit to a surviving unit.

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Netgear GS728TP Manual do Utilizador Página 71