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  • 1. Chapter 8: Local Area Networks: Internetworking
  • 2. Objectives
    • List the reasons for interconnecting multiple local area network segments and interconnecting local area networks and wide area networks
    • Identify the functions and purposes of the various interconnection devices that have been used over time
    • Define a hub and describe the situations in which a hub is used
    • Describe how a transparent bridge learns
  • 3. Objectives (continued)
    • Describe what a switch is and how it differs from other devices
    • Describe the types of situations in which using a switch is advantageous
    • Describe what a router is and how it differs from other devices
    • Describe the types of situations in which a router is used
  • 4. Introduction
    • Sometimes necessary to connect local area network to another LAN or to wide area network
    • Local area network to local area network connections often performed with bridge-like device
    • Local area network to wide area network connections usually performed with router
    • Switch - can be used to interconnect segments of a local area network
  • 5. Why Segment or Internetwork Local Area Networks?
    • To separate / connect one corporate division with another
    • To connect two LANs with different protocols
    • To connect a LAN to the Internet
    • To break a LAN into segments to relieve traffic congestion
    • To provide a security wall between two different types of users
  • 6. Hubs
    • Hub - interconnects two or more workstations into a local area network
    • When workstation transmits to a hub
      • Hub immediately resends data frame out to all connecting links
    • Hub can be managed or unmanaged
      • Managed hub possesses enough processing power that it can be managed from a remote location
  • 7. Bridges
    • A bridge (or bridge-like device)
      • Can be used to connect two similar LANs, such as two CSMA/CD LANs
      • Can also be used to connect two closely similar LANs, such as a CSMA/CD LAN and a token ring LAN
      • Examines destination address in a frame
        • Either forwards this frame onto next LAN or does not
      • Examines source address in frame
        • Places this address in a routing table to be used for future routing decisions
  • 8. Bridges (continued)
  • 9. Transparent Bridge
    • Does not need programming
    • Observes all traffic  builds routing tables
      • This observation is called backward learning
    • Each bridge has two connections (ports)
      • Routing table associated with each port
  • 10. Transparent Bridge (continued)
    • Bridge
      • Observes each frame that arrives at port
      • Extracts the source address from the frame
      • Places that address in the port’s routing table
    • Transparent bridge is found with CSMA/CD LANs
  • 11. Transparent Bridge (continued)
  • 12. Transparent Bridge (continued)
  • 13. Transparent Bridge (continued)
    • Transparent bridge can also convert one frame format to another
    • Note that some people / manufacturers call this kind of bridge a gateway or router
    • Bridge
      • Removes headers and trailers from one frame format
      • Inserts (encapsulates) headers and trailers for second frame format
  • 14. Remote Bridge
    • Capable of passing data frame from one local area network to another when
      • Two LANs are separated by long distance
      • There is a wide area network connecting the two LANs
    • Remote bridge takes the frame before it leaves the first LAN
      • Encapsulates the WAN headers and trailers
    • When packet arrives at destination remote bridge  that bridge removes the WAN headers and trailers leaving original frame
  • 15. Remote Bridge (continued)
  • 16. Switches
    • Combination of hub and bridge
    • Can interconnect two or more workstations
    • Like bridge, it observes traffic flow and learns
    • When a frame arrives at a switch, the switch
      • Examines destination address
      • Forwards frame out the one necessary connection
    • Workstations that connect to
      • Hub  on shared segment
      • Switch  on switched segment
  • 17. Switches (continued)
  • 18. Switches (continued)
    • Backplane of a switch is fast enough to support multiple data transfers at one time
    • A switch that employs cut-through architecture is passing on the frame before the entire frame has arrived at the switch
  • 19. Switches (continued)
    • Multiple workstations connected to a switch use dedicated segments
      • Very efficient way to isolate heavy users from the network
    • A switch can allow simultaneous access to multiple servers, or multiple simultaneous connections to a single server
  • 20. Switches (continued)
  • 21. Isolating Traffic Patterns and Providing Multiple Access
  • 22. Isolating Traffic Patterns and Providing Multiple Access (continued)
  • 23. Isolating Traffic Patterns and Providing Multiple Access (continued)
  • 24. Isolating Traffic Patterns and Providing Multiple Access (continued)
  • 25. Full-Duplex Switches
    • Allows for simultaneous transmission and reception of data to and from a workstation
    • This full duplex connection helps eliminate collisions
    • To support a full duplex connection to a switch, at least two pairs of wires are necessary
      • One for the receive operation
      • One for the transmit operation
    • Most people install four pairs today, so wiring is not problem
  • 26. Full-Duplex Switches (continued)
  • 27. Network Servers
    • Network servers provide necessary storage for LAN software
    • Usually focal point for network operating system
    • Increasingly, network servers are functioning as bridges, switches, and routers
    • By adding appropriate card, a server can assume multiple functions
  • 28. Routers
    • Router - device that connects a LAN to a WAN or a WAN to a WAN
    • Router:
      • Accepts outgoing packet
      • Removes any LAN headers and trailers
      • Encapsulates necessary WAN headers and trailers
    • Because router has to make wide area network routing decisions  router has to dig down into the network layer of the packet to retrieve network destination address
  • 29. Routers (continued)
    • Routers are often called “layer 3 devices”
      • Operate at the third layer, or OSI network layer, of the packet
    • Often incorporate firewall functions
  • 30. Routers (continued)
  • 31. LAN Internetworking in Action: A Small Office Revisited
    • Recall In Action example from Chapter Seven
    • A small office with 20 workstations in one room and 15 workstations in another room were connected to a server via 100BaseTX
    • One hub was kept in a closet near the 20 workstations while a second hub was near the server
  • 32. LAN Internetworking in Action: A Small Office Revisited (continued)
  • 33. LAN Internetworking in Action: A Small Office Revisited (continued)
    • Now Hannah wants to connect the LAN to the Internet
    • She adds a router next to the server and connects it to the hub
    • She connects the router to a high-speed telephone line such as a T-1 service
    • She will also have to program the router to perform IP addressing and firewall functions
  • 34. LAN Internetworking in Action: A Small Office Revisited (continued)
  • 35. LAN Internetworking in Action: A Small Office Revisited (continued)
    • Now network usage is so high that Hannah must consider segmenting the network
    • She decides to install a database server near the original server and replace both hubs with switches
  • 36. LAN Internetworking in Action: A Small Office Revisited (continued)
  • 37.
    • Interconnecting multiple LAN segments as well as LANs and WANs
    • Interconnection devices
    • Hubs
    • Transparent bridges
    • Switches
    • Routers
    Summary