1Internetworking (Part II)School of BusinessEastern Illinois University © Abdou Illia, Fall 2014(September 22, 2014)2Learning Objectives Understand internetworking devices operation– Source-routing bridge– Remote bridge– Router– Hubs and switches3Source-routing BridgesWhen a workstation wants to send a frame:It must know the exact path of network / bridge / network / bridge / network …If a workstation does not know the exact path, it sends out a discovery frame.The discovery frame makes its way to the final destination, then as it returns, it records the path. Found with token ring networks Do not learn from observing traffic324Remote Bridges Used to (remotely) connect two LANs– separated by a long distance– Passing by a Wide Area NetworkRemote BridgeLANWA NRemote BridgeLAN5Remote BridgesA remote bridge takes the frame before it leaves the first LAN and encapsulates it with WAN header and trailerWhen the packet arrives at the destination remote bridge, that bridge removes the WANheader and trailer leaving the original frame.WA N56Remote Bridges Different LANs protocols (100BaseT, 100BaseFX Ethernet, Token Ring, etc.) Different WANs standards (X.25,Frame Relay, ATM, etc.)  Unique Remote bridge for each pair of LAN-WAN combination637Question Your supervisor at Network Inc. wants you to provide your expertise to help a client decide what kind of bridge is needed to interconnect two LANs located in two separate buildings in town. One of the LANs uses CSMA/CD and the other one is a Token Ring LAN. What will be your recommendation?a) Use a Source-Routing bridgeb) Use a Transparent bridgec) Use a Transparent bridge, but check the features to make sure that it has the appropriate conversion function.d) Use a Remote bridge.8Routers 3-Layer device that connects:– a LAN to a WAN– a WAN to a WAN (or used to forward messages in a WAN)– LANs to LANs too Functions:– Conversion between frame formats– Forwarding frames– Making routing decisions– Often firewall functions (protection)9Routers1. Receives a frame with a CSMA/CD format2. Removes the CSMA/CD header and Trailer (Deencapsulation)3. Encapsulates the WAN’s header and Trailer4. Sends the frame into the WAN410Routers Like bridges, routers have incoming and outgoing ports Frame arrives at incoming portData Link Data LinkNetwork/InternetIncoming FrameFirst Router• 3-Layer devices11Routers Incoming Data Link on the Router– Removes the LAN’s Header & Trailer to access the Network/Internet Layer’s packet (deencapsulation)– Passes the removed packet to the router’ Network/Internet layerData Link Data LinkNetwork/InternetPacketFirst RouterIncoming Port on First RouterIncoming Frame12Routers Since the Network/Internet layer is the highest layer on a router– Network/Internet layer decides where to send the packet next: another router or the destination LANData Link Data LinkNetwork/InternetFirst Router513Layer Cooperation on the First Router Network/Internet layer passes Network/Internet packet to Data Link layer on the selected outgoing port that will carry the packet to the next router or the destination LANData Link Data LinkNetwork/InternetFirst RouterPacketSelected Outgoing Port on First Router14Layer Cooperation on the First Router The Data Link layer on the selected port creates a Frame including the packet, a Header and a Trailer The created frame is passed to the Physical layer on the selected port for transmission to the next router (or destination LAN)Net./InternetData LinkNet./InternetData LinkFrameSelected Outgoing PortOn First RouterIncoming PortOn Next RouterPhysicalLayer151.Station A transmitsto the Hub2.Hub broadcaststo all stationsStation C must wait,or its signal willcollide with Station A'ssignalStationAStationBStationCStationAStationBStationCHub operationHubs split available bandwidth among computers, i.e. with a 100 Mbps hub, the network speed will be 100 Mbps / n (where n is the number of computers)Active hubs include repeater capabilities for regenerating signals.Passive hubs don't regenerate signals. Limited to a 30meter distance apart from computers.(Except sending station)616Hubs1.Station A transmitsto the Hub2.Hub broadcaststo all stationsStation C must wait,or its signal willcollide with Station A'ssignalStationAStationBStationCStationAStationBStationC A hub interconnects stations in Star-Bus LANs A hub works at the physical layer (Accepts & forward frames) A hub broadcasts frames out all connecting links (except sender’s link) A hub could be used to create logical LAN segments for congestion relief17SwitchesStationCStationDSwitchStationBStation ATransmitsto Station CSwitch SendsSignal out aSingle Port162345StationAStation BTransmitsSimultaneouslyto Station D A switch examines the destination address and forwards the frame outthe one necessary connection. Multiple stations connected to a switch use dedicated segments i.e. eachstation has a private dedicated connection to the switch A hub could be used to create logical LAN segments for congestion reliefSwitching tableMAC Address PortA1-44-D55-1F-AA-4C 1 (Station A)B2-CD-13-5B-E4-65 2 (Station B)C3-2D-55-3B-A9-4F 5 (Station C);;18Hubs and SwitchesUsing switches and hub for interconnecting LAN’s segmentsCrossover cable is used to connect hub and/or switches719Summary Questions1. How a Source-routing bridge differ from a transparent bridge ? 2. What is the purpose of a discovery frame ?3. In what situations is a Remote bridge used? 4. What are the basic functions of a router?5. What is a crossover cable?20Summary Questions1. The local area network shown in Figure 8-18 (p. 261) has two hubs (X and Y) interconnecting the workstations and servers. What workstations and servers will receive a copy of a packet if the following workstations/servers transmit a message:Workstation 1 sends a message to workstation 3:Workstation 2 sends a message to Server 1:Server 1 sends a message to workstation 3:2. Replace hub Y with a switch. Now, what workstations and servers will receive a copy of a packet if the following workstations/servers transmit a message:Workstation 1 sends a message to workstation 3:Workstation 2 sends a message to Server 1:Server 1 sends a message to workstation 3:21Summary Questions3. Do Internetworking Exercise