28. Spanning Tree
ROX™ v2.2 User Guide 308 RuggedBackbone™ RX1500
5. Identify desired steady state topology.
Identify the desired steady state topology taking into account link speeds, offered traffic and QOS.
Examine of the effects of breaking selected links, taking into account network loading and the
quality of alternate links.
6. Decide upon port cost calculation strategy.
Select whether fixed or auto-negotiated costs should be used? Select whether the STP or RSTP
cost style should be used.
7. Calculate and configure priorities and costs.
8. Implement the network and test under load.
28.3.2. RSTP in Ring Backbone Configurations
RSTP may be used in ring backbone configurations where rapid recovery from link failure is required.
In normal operation, RSTP will block traffic on one of the links, for example as indicated by the double
bars through link H in Figure 28.4, “Example of a Ring Backbone Configuration”. In the event of a failure
on link D, bridge 444 will unblock link H. Bridge 333 will communicate with the network through link F.
Figure 28.4. Example of a Ring Backbone Configuration
Procedure 28.2. Design Considerations for RSTP in Ring Backbone Configurations
1. Select the design parameters for the network.
What are the requirements for robustness and network fail-over/recovery times? Typically, ring
backbones are chosen to provide cost effective but robust network designs.
2. Identify required legacy support and ports with half-duplex/shared media restrictions.
These bridges should not be used if network fail-over/recovery times are to be minimized.
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