Internetworking devices(networking)

1© 2009, Cisco Systems, Inc. All rights reserved.

Module 2Internetworking Devices

By Dr. Percy DIAS

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Physical Topology

• Physical topology is the actual layout of the wire or media.

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Physical Topology • Bus

–Connects all the devices using a single cable

–Main cable segment must end with a terminator that absorbs the signal when it reaches the end (data can bounces back)

• Star –Most commonly used in Ethernet LAN

–Central connection point can be a hub, switch or router, and might be desirable for security or restricted access

–If the central device fails, the whole network becomes disconnected

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Physical Topology

• Ring–Frame travels around the ring, stopped at each node

–If a node wants to transmit data, it is permitted to add data as well as destination address

–Each device cleans up the signal, so fewer repeaters are needed

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Physical Topology• Dual Ring

–If one ring fails, data can be transmitted on the other ring

• Full-mesh–Connect all devices to each other for redundancy and fault tolerance

• Partial-mesh–At least one device maintains multiple connections to others

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Logical Topology• Logical topology of a network refers to the

logical paths that signals travel from one point on the network to another

• Broadcast– Ethernet

• Token Passing– Controls network access by passing an

electronic token sequentially to each host– Token Ring and FDDI are examples of Token

Passing on a physical ring topology

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Collisions

• Hubs operate at Layer 1, simply repeating all received signals out all other ports

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Networking Devices

• End user devices– Provide services directly to the user

• Network devices– Connect the end-user devices to allow

them to communicate

• Data leaves a source and it is transformed into either electrical , light pulse or radio waves (signals) that pass along the medium

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Networking Devices

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Repeated Ethernet Signal

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Repeated Ethernet Signal

• Betty sends a clean signal

• The signal degrades by the time it reaches the repeater

• The repeater regenerates a new, clean signal and sends it out its other port

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Repeaters

• When a signal is sent over a wire, it degrades• To extend the distance of LANs, repeaters were

developed• Typically had two ports connecting two different

Ethernet segments• Interpreted the incoming signal on one port as

1’s and 0’s• Sent a regenerated clean signal out the other

port

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Repeaters: Layer 1

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Hubs

• Regenerate signals

• Used as network concentration points

• Multiport repeater

• Layer 1 device

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Hub Operation

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Network Interface Card • Carries a unique code called a Media

Access Control (MAC)• MAC address controls data communication

for the host on the network• NICs are considered layer 2 and operate at

both layer 1 and 2 (Layer 1: send and receive signals over an attached cable)

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Bridges

Layer 2 device designed to create two or more LAN segments, each of which is a separate collision domain

Bridges filter traffic by looking at MAC

addresses.

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Bridges • Filter traffic on a LAN to keep local traffic local

yet allow connectivity to other parts

• Keep track of which MAC addresses are on each side of the bridge and makes forwarding decisions based on MAC address table

• When a bridge receives a frame, the destination MAC address is looked up in the bridge table to determine whether to filter, flood or forward the frame onto another segment.

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Bridges

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Flooding Unknown Unicasts

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Learning Table Entries and Flooding Unknown Unicasts

• Switches and bridges learn entries in the table dynamically

• They use this logic:– Examine the source MAC address of the

frame and the interface on which it was received

– Add that source MAC address and corresponding interface to the table

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Learning Content Addressable Memory (CAM) Table Entries: Two Switches

SW2

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Bridge Making Filter Decision

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Bridge Making a Forwarding Decision

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LAN Switches

• Layer 2 device• Use a table of MAC addresses (switching table) to

determine the segment on which a frame needs to be transmitted

• Cisco switching table sometimes referred to as Content Addressable Memory (CAM).

• Switches operate at much higher speed than bridges (hardware vs software)

• Each switch port acts as a separate bridge and give each host the medium’s full bandwidth (microsegmentation)

• Improve network performance: speed and bandwidth

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Switch Making a Forwarding Decision

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Switch Buffering Example

Barney

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Preventing Collisions with Switch Buffering

• Switches prevent collisions by buffering frames

• If several PCs send frames to the same address at the same time, the switch holds the frames in memory - a process called buffering

• The switch then forwards the frames one at a time

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Routers

• Layer 3 device

• Use logical address (network layer address)

• Can connect different layer 2 technologies

• Examine incoming packet (layer 3 data), choose the best path, and switch them to the proper outgoing port.

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Cisco Academy 3 Reference

• CCNA1 Online Materials• Slide 2 - 6: 2.1.4• Slide 8-9, 26: 2.1.3• Slide 12-14: 5.1.6-5.1.7• Slide 16-19, 23-24, 26: 5.1.9-5.1.11

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Cisco Academy 4 Exploration Reference

Networking Fundamentals• Slide 2 - 6: 9.1.1-9.1.3• Slide 8-9,12-14, 26: 9.6.1-9.6.4• Slide 16-19, 23-24, 26: 9.6.1-9.6.4• Slide 14-15: 9.6.1-9.6.2