Semester 3

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• Semester 3LAN Switching
• Chapter 2

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Objectives

• By the end of this chapter we will be able to
  perform tasks related to
• Various LAN Communication Problems
• Full-Duplex transmitting, Fast Ethernet, and LAN
  Segmentation.
• Switching and VLANs
• The Spanning Tree Protocol.

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Elements of Ethernet 802.3 Networks

• The data frame broadcast delivery nature of
  Ethernet/802.3 LANs.
• Carrier sense multiple access collision detect
  (CSMA/CD) access methods allowing only one
  station to transmit at a time.
• Multimedia applications with higher bandwidth
  demand such as video and the Internet, coupled
  with the broadcast nature of Ethernet, can create
  network congestion.
• Normal latency as the frames travel across the
  Layer 1 medium and through Layer 1, 2, and 3
  networking devices, and the latency added by the
  extension of Ethernet/802.3 LANs by adding
  repeaters.
• Extending the distances of the Ethernet/802.3
  LANs by using Layer 1 repeaters.

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Elements of Ethernet 802.3

• One of the inherent problems with CSMA/CD
  technology is collisions.
• All Devices are connected to same delivery
  medium.

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Half-Duplex Ethernet Operation

1. NIC sends a frame.
2. NIC Loops the sent frame into its receive pair.
3. The hub receives the frame.
4. The hub sends the frame across an internal bus.
5. The hub repeats the signal out to all other
   devices.

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Half Duplex Ethernet

• Receive Rx. (Pin 2, 6 orange, green)
• Transmit TX. (Pin 1,3 WOrange, WGreen)
• Loop Back.
• Collision Detection.
• Jam Signal .
• Backoff Algorithm.

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Full-Duplex Ethernet

• Frames that are sent can not collide with frames
  being received no collisions are possible.
• Loop back and collision segments are omitted.
• Waiting for others to send their frames is not
  necessary because there is only one sender for
  each twisted pair.
• There is 10 Mbps in each direction, increasing
  the available band width.
• Requirements NIC with Full-Duplex capability,
  Ethernet switch transmission and receipt of data
  occurs on separate non-competitive circuits.

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Fast Ethernet

• Two main features of Fast Ethernet
• Faster speed.
• Auto Negotiation
• Requirements
• Fast switch port
• Fast NIC

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Ethernet LAN SegmentationCCNA Objectives

• Describe LAN segmentation using bridges,
  switches, and routers.
• Describe network congestion problem in Ethernet.
• Describe the benefits of network segmentation
  with bridges, switches and routers.
• Describe the advantage of LAN Segmentation

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LAN Segmentation Using Bridges

• Transparent bridging the process of forwarding
  frames when appropriate. To accomplish this,
  transparent bridges perform three key functions
• Learning MAC addresses by examining the source
  MAC address of each frame received by the bridge.
• Deciding when to forward a frame and when to
  filter a frame, based on the destination MAC
  address.
• Creating a loop-free environment with other
  bridges using the Spanning-Tree Protocol.

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LAN Segmentation Using Bridges
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Characterizations of transparent bridge

• Broadcast and multicast frames are forwarded by a
  bridge.
• Bridges perform switching of frames using layer 2
  headers, and are layer 3 protocol-independent.
• Store and forward operation is typical in
  transparent bridging devices.
• The transparent bridge must perform processing on
  the frame, which also can increase latency(as
  compared to a single LAN Segment.

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LAN Segmentation Using a Switch

• An Ethernet Switch uses the same logic as a
  transparent bridge. However the internal logic
  of the switch is optimized for performing the
  basic function of choosing when to forward and
  when to filter a frame. (Switched Fabric). The
  basic logic of a LAN switch is as follows
• A frame is received.
• If the destination is a broadcast or multicast,
  forward on all ports.
• If the destination is a unicast and the address
  is not in the address table, forward on all
  ports.
• If the destination is a unicast and the address
  is in the address table, forward the frame out
  the associated port

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LAN Segmentation Using a Switch.
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Characteristics of LAN Segmentation Using a Switch

1. The two ARP broadcasts (Steps 1 and 5) are sent
   out all switch ports because switches and bridges
   do not perform the broadcast fire wall function.
2. After the switching table is built, the switch
   forwards unicasts only out of the appropriate
   ports.
3. The switch network has created three separate
   Ethernet segments. Each segment is called a
   collision domain.

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Collision Domains-Bridges VS. Switches
A collision domain is a set of interface cards
(NICs) for which a frame sent by one NIC could
result in a collision with a frame sent by any
other NIC in the collision domain.
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Switch Internal Processing
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LAN Segmentation Using a Router
The ARP broadcasts are not forwarded by the
router. Communicating with a different segment
will result on saving one MAC address on the
clients ARP table The routers
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Broadcast Domains
A broadcast domain is a set of NICs for which a
broadcast frame sent by one NIC will be received
by all other NICs in the broadcast domain.
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Comparison of Segmentation Option