Allied-telesis AT-S62 Bedienungsanleitung PDF herunterladen (Seite 488)

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Chapter 22: Spanning Tree and Rapid Spanning Tree Protocols

488 Section IV: Spanning Tree Protocols

Forwarding Delay and Topology Changes

If there is a change in the network topology due to a failure, removal, or

addition of any active components, the active topology also changes. This

may trigger a change in the state of some blocked ports. However, a

change in a port state is not activated immediately.

It might take time for the root bridge to notify all bridges that a topology

change has occurred, especially if it is a large network. If a topology

change is made before all bridges have been notified, a temporary data

loop could occur, and that could adversely impact network performance.

To forestall the formation of temporary data loops during topology

changes, a port designated to change from blocking to forwarding passes

through two additional states—listening and learning—before it begins to

forward frames. The amount of time a port spends in these states is set by

the forwarding delay value. This value states the amount of time that a

port spends in the listening and learning states prior to changing to the

forwarding state.

The forwarding delay value is adjustable in the AT-S62 management

software. The appropriate value for this parameter depends on a number

of variables, the size of your network being a primary factor. For large

networks, you should specify a value large enough to allow the root bridge

sufficient time to propagate a topology change throughout the entire

network. For small networks, you should not specify a value so large that a

topology change is unnecessarily delayed, which could result in the delay

or loss of some network traffic.

Table 16. Port Priority Value Increments

Increment

Port

Priority

Increment

Port

Priority

008128

1 16 9 144

2 3210160

3 48 11 176

4 6412192

5 8013208

6 9614224

7 112 15 240

1 2 ... 483 484 485 486 487 488 489 490 491 492 493 ... 821 822

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