1 © 2009, Cisco Systems, Inc. All rights reserved. Module 2 Internetworking Devices By Dr. Percy DIAS
Jan 28, 2015
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