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Unit 5: Networking Devices




          In this manner the computers on segment 3 will receive duplicate packets. In case of large  Notes
          networks some segments may receive many packets and thus causing looping.
          A loop, therefore, can cause a broadcast packet or a packet with an unknown destination to
          circulate through it, thus rendering the network inoperable. This condition is avoided by making
          some bridges not to forward frames. An algorithm known as Distributed Spanning Tree (DST)
          accomplishes this task. This algorithm decides which bridge should forward the packets in the
          network. Under this scheme bridges exchange a control message known as a hello message to
          select a single transmission route. Remaining bridges maintain a standby position and provide
          alternate path in case of the some bridge fails in the selected transmission path. In Figure 5.8
          bridge connecting segment 1 and 3 will be active only if the bridge connecting segment 2 and 3
          fails otherwise it acts as a standby bridge for network. In other words, bridges that support the
          spanning tree algorithm have the ability to automatically reconfigure themselves for alternate
          paths if a network segment fails, thereby improving overall reliability.

          IBM Source Routing Protocol (SRP) Bridge: These are programmed with specific routes for each
          packet based on considerations such as the physical location of the nodes, and the number of
          bridges involved.
          Source Routing Transparent (SRT): It is defined in the IEEE 802.1 standard. It is effectively a
          combination of STP and SRP. The SRT router can connect LANs by either method, as programmed.

          5.2.2 Classification of Bridges


          These are classified into local and remote bridges:
               Local brides are ordinary bridges
               Remote bridges are used to connect networks that are far from each other. A WAN is
               generally provided between two bridges.
          Figure 5.8 shows the local and remote bridge connection.

                                  Figure 5.8: Local and Remote Bridge

                                                Local
                                                Bridge






                                  Remote                   Remote

                                  Bridge                   Bridge

                                               WAN

                                          Leased Line or ISDN etc.





              Task  What are bridges? What are different types of bridges?





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