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Lecture 7 internetworking
 

Lecture 7 internetworking

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  • GMU - IT 481, Spring 2006 1/23/2006

Lecture 7 internetworking Lecture 7 internetworking Presentation Transcript

  • Hemang Kothari Assistant Professor Computer Engineering Department MEFGI, Rajkot. Email: hemang.kothari@marwadieducation.edu.in Internetworking Devices
  • Internetworking Devices • Internetworking devices are products used to connect networks. • As computer network grows in size and complexity, so do the internetworking devices used to connect them. Broadly, following are the Internetworking devices: • Repeaters • Hubs • Bridges • Switches • Routers • Gateways
  • • Networking devices are used to construct networks. • Example: A local area Network (LAN) may need to cover more distance that its media can handle effectively. In this case, you can use a repeater to regenerate the signal.
  • • Internetworking devices are used to connect networks. • Example: If you want to link a LAN into an internet, you need an internetworking device as a router or a gateway. • An internet is an interconnection of individual networks.
  • Connecting Devices and the OSI Model
  • Connecting Devices
  • Connecting DevicesConnecting Devices Repeaters Hubs Bridges Two-Layer Switches
  • Connecting devices
  • Repeaters • A repeater (or regenerator) is an electronic device that operates on only the physical layer of the OSI model. • A repeater installed on a link receives the signal before it becomes too weak or corrupted, regenerates the original pattern, and puts the refreshed copy back on the link.
  • Repeaters • A repeater does not actually connect two LANS; it connects two segments of the same LAN. • A repeater forwards every frame; it has no filtering capability.
  • Hubs • A Hub is a multiport repeater. It is normally used to create connections between stations in a physical star topology.
  • Bridges • Bridges operate in both the physical and the data link layers of the OSI model.
  • Bridges • Bridges can divide a large network into smaller segments. They contain logic that allows them to keep the traffic on each segment separate. When a frame (or packet) enters a bridge, the bridge not only regenerates the signal but checks the destination address and forwards the new copy only to the segment the address belong.
  • Bridges • A bridge operates in both the physical and the data link layers. • As a physical layer device, it regenerates the signal it receives. • As a data link layer device, the bridge can check the physical (MAC) address (source and destination) contained in the frame. • A bridge has filtering capability. It can check the destination address of a frame and decide if the frame should be forwarded or dropped. If the frame is to be forwarded, the decision must specify the port. • A bridge does not change the physical (MAC) addresses in a frame. • A bridge has a table used in filtering decisions.
  • Bridge
  • Types of Bridges • To select between segments, a bridge must have a look-up table that contains the physical addresses of every station connect to it. The table indicate to which segment each station belongs. Simple Bridge • The address table must be entered manually, before a simple bridge can be used. • Whenever a new station is added or removed, the table must modified. • Installation and maintenance of simple bridges are time- consuming and potentially more trouble than the cost savings are worth.
  • Types of Bridges Multiport bridges A multiport bridge can be used to connect more than two LANs.
  • Transparent Bridges • A transparent, or learning, bridge builds its table of station addresses on its own as it performs its bridge functions. • If a transparent bridge is added or removed from the system, reconfiguration of the stations is unnecessary. • A transparent bridge must meet following criteria: 1. Frames must be forwarded from one station to another. 2. The forwarding table is automatically made by learning frame movements in the network.
  • Learning Bridge
  • Loop Problem • Transparent bridges work fine as long as there are no redundant bridges in the system. • Bridges are normally installed redundantly, which means that two LANs may be connected by more than one bridge. In this case, if the bridges are transparent bridges, they may create a loop, which means a packet may be going round and round, from one LAN to another and back again to the first LAN. • To solve the looping problem, the IEEE specification requires that bridges use the spanning tree algorithm to create a loopless topology.
  • Spanning Tree • A spanning tree is a graph in which there is no loop. • In a bridged LAN, a loopless topology means a topology in which each LAN can be reached from any other LAN through one path only (no loop). • It is not possible to change the physical topology of the system, but we can create a logical topology that overlays the physical one.
  • Source Routing • Another solution to prevent loops in LANs connected by bridges is source routing. • In this method, the source of the packet defines the bridges and the LANs through which the packet should go before reaching the destination
  • Routers • Routers have access to network layer addresses and contain software that enables them to determine which of several possible paths between those addresses is the best for a particular transmission. • Routers operate in the physical, data link, and network layers of the OSI model.
  • • Routers relay packets among multiple interconnected networks. They route packets from one network to any of a number of potential destination networks on an internet.
  • Gateways • Gateways potentially operate in all seven layers of the OSI model.
  • Gateways • A gateway is a protocol converter. A router by itself transfers, accepts, and relays packets only across networks using similar protocols. • A gateway can accept a packet formatted for one protocol (e.g. AppleTalk) and convert it to a packet for another protocol (e.g. TCP/IP).
  • Gateways • A gateway is generally software installed within a router. The gateway understands the protocols used by each network linked into the router and is therefore able to translate from one to another.