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How STP Works 37If a link failure is detected, as shown in Figure 10, the STP processreconfigures the network so that traffic from LAN segment 2 flowsthrough Bridge B.Figure 10 Traffic flowing through Bridge BSTP determines which is the most efficient path between each bridgedsegment and a specifically assigned reference point on the network. Oncethe most efficient path has been determined, all other paths are blocked.Therefore, in Figure 8, Figure 9, and Figure 10, STP initially determinedthat the path through Bridge C was the most efficient, and so blockedthe path through Bridge B. After the failure of Bridge C, STP re-evaluatedthe situation and opened the path through Bridge B.How STP Works When enabled, STP determines the most appropriate path for trafficthrough a network. It does this as outlined in the sections below.STP Requirements Before it can configure the network, the STP system requires:■ Communication between all the bridges. This communication iscarried out using Bridge Protocol Data Units (BPDUs), which aretransmitted in packets with a known multicast address.■ Each bridge to have a Bridge Identifier. This specifies which bridge actsas the central reference point, or Root Bridge, for the STP system —the lower the Bridge Identifier, the more likely the bridge is to becomethe Root Bridge. The Bridge Identifier is calculated using the MACaddress of the bridge and a priority defined for the bridge. The defaultpriority of your Switch is 32768.