Chapter 8: Local Area Networks: Internetworking

Data Communications and Computer Networks: A Business User’s Approach Third Edition Chapter 8: Local Area Networks: Internetworking

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Bridges (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Transparent Bridge (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Remote Bridge (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Switches (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Switches (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

Isolating Traffic Patterns and Providing Multiple Access Data Communications & Computer Networks: A Business User's Approach, Third Edition

Isolating Traffic Patterns and Providing Multiple Access (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Full-Duplex Switches (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Routers (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

LAN Internetworking in Action: A Small Office Revisited (continued) Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

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 Data Communications & Computer Networks: A Business User's Approach, Third Edition

Summary • Interconnecting multiple LAN segments as well as LANs and WANs • Interconnection devices • Hubs • Transparent bridges • Switches • Routers Data Communications & Computer Networks: A Business User's Approach, Third Edition

Chapter 8: Local Area Networks: Internetworking