5-12 C HAPTER 5: A DVANCED M ANAGEMENTSpanning Tree ProtocolUsing the Spanning Tree Protocol (STP) functionalityof your Switch makes your network more fault toler-ant.The following sections explain more about STP andthe STP features supported by the Switch.STP is not currently supported over an AsynchronousTransfer Mode (ATM) network. Therefore, if youhave an ATM OC-3c Module installed in yourSwitch, it does not join the STP system.What is STP?STP is a part of the 802.1d bridge specificationdefined by the IEEE Computer Society. To explainSTP more effectively, the Switch 1000 will bedefined as a bridge.STP is a bridge-based system for providing fault tol-erance on networks. STP allows you to implementparallel paths for network traffic, and ensure that:n Redundant paths are disabled when the mainpaths are operationaln Redundant paths are enabled if the main pathsfailAs an example, Figure 5-10 shows a network con-taining three LAN segments separated by threebridges. With this configuration, each segment cancommunicate with the others using two paths. Thisconfiguration creates loops which cause the net-work to overload; however, STP allows you to havethis configuration because it detects duplicate pathsand immediately prevents, or blocks, one of themfrom forwarding traffic.Figure 5-11 shows the result of enabling STP on thebridges in the configuration. The STP system hasdecided that traffic from LAN segment 2 to LANsegment 1 can only flow through Bridges C and A.If the link through Bridge C fails, as shown inFigure 5-12, the STP system reconfigures the net-work so that traffic from segment 2 flows throughBridge B.
