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Networking and Internetworking Deviceswe need networking and internetworking devices to extend physical distance and to improve efficiency and manageability

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Introduction

Many times it is necessary to connect a local area network to another local area network or to a wide area network.

Local area network to local area network connections are often performed with a bridge.

Local area network to wide area network connections are usually performed with a router.

A third device, the switch, can be used to interconnect segments of a local area network.

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Why Interconnect?

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.

To connect WLAN to LAN

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Networking and Internetworking DevicesConnecting devices and the OSI Model

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Repeatersoperate on physical layerregenerate the original bit pattern (which may become too weak or corrupted) and put the refreshed copy back onto the linkallow us to extend only the physical length of a network

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RepeatersA repeater in the OSI model

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Repeatersfunction of a repeater a repeater is a regenerator, not an amplifier

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Bridgesoperate in physical and data link layersdivide a large network into smaller segmentsrelay frames between two originally separate LANs

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BridgesA bridge in the OSI model

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Bridgescontain logic that allows them to keep the traffic for each segment separatefilter traffic – useful for controlling congestion and isolating problem linkswhen a frameenters a bridge,checks addressand forwards tothe right segment

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BridgesTypes of Bridges simple bridges – most primitive, least expensive,

addresses must be entered manually for each segment

multiport bridges – can connect more than one LANs

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BridgesTypes of Bridges (cont) transparent bridges – build table of station

addresses dynamically by checking source and destination addresses, self updating

to prevent loops in the LANs connected by several bridges spanning tree algorithm and source routing is used

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BridgesBridges can connect LANs using different protocols at the data link layer; issues considered frame format payload size data rate address bit order access method, etc

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Routersoperate in physical, data link and network layers of the OSI modelrelay packets among multiple interconnected networksby default is a single-protocoldevice

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Routersrouters in an internet routers act like stations on a network, have several

addresses on and link to two or more networks at thesame time

packets received will be relayedto the adjacent network or passed them onto another router

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Gatewaysoperate in all seven layers of the OSI

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Gatewaysa gateway is a protocol converter accept a packet formatted for one protocol (e.g.

AppleTalk) and convert it to a packet formatted for another protocol (e.g. TCP/IP)

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Other devicesMultiprotocol routers designed to route packets belonging to two or

more protocols (e.g. IP, IPX, AppleTalk) single protocol versus

multiprotocol routers:

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Other devicesBrouters a single-protocol or multiprotocol routers that acts

as a router and sometime as a bridge

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Other devicesSwitches provide bridging

functionality withgreater efficiency

store-and-forward switch cut-through switch

Routing Switches use network layer destination address to find the

output link to which the packet should be forwarded

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Routing Algorithmscommon methods used to calculate the shortest path between two routers distance vector routing

each router periodically shares its knowledge about the entire network with its neighbors

link state routing each router shares its

knowledge of its neighbor with all routers in the internetwork

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Routing AlgorithmsDistance Vector Routing the concept

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Routing AlgorithmsDistance Vector Routing (cont) routing table

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Routing AlgorithmsDistance Vector Routing (cont) routing table distribution

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Routing AlgorithmsDistance Vector Routing (cont) updating routing table for router A

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Routing AlgorithmsDistance Vector Routing (cont) final routing table

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Routing AlgorithmsDistance Vector Routing (cont) Updating algorithm

1. If the advertised destination table is not in the routing table, the routershould add the advertised information to the table

2. If the advertised destination is in the routing table, a. if the next hop field is the same, the router should

replace the entry in the table with the advertised one b. if the next hop field is not the same

i. if the advertised hop count is smaller than the one in the table, the router should replace the entry in the table with the new one

ii. if the advertised hop count is same or larger, the router should do nothing

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Routing AlgorithmsDistance Vector Routing (cont) Example