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ROS™ v3.5 144 RS400
notifications in the network. Ports with half duplex/shared media restrictions require special
attention in order to guarantee that they do not cause extended failover/recovery times.
4. Choose the root bridge and backup root bridge carefully.
The root bridge should be selected to be at the concentration point of network traffic. Locate the
backup root bridge adjacent to the root bridge. One strategy that may be used is to tune the
bridge priority to establish the root bridge and then tune each bridge’s priority to correspond to
its distance from the root bridge.
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.
5.3.2 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 97. 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 97: Example of a Ring Backbone Configuration