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Ethernet

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Ethernet

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Ethernet

  1. 1. Ethernet Network Fundamentals – Chapter 9 ITE I Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1
  2. 2. Objectives  Identify Ethernet  Identify the function and characteristics of the media access control method used by Ethernet protocol.  Identify different types of layer 2 addressing and impacts network operation and performance.  Identify the application and benefits of using Ethernet switches in a LAN as opposed to using hubs.  Identify basic switch operations  Identify the ARP process. ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 2
  3. 3. What is Ethernet?  A family of LAN products described by the IEEE standards  Developed in the early 1980s and first published by the consortium Digital equipment, Intel and Xerox (DIX) as an open standard  To maintain compatibility with the ISO the IEEE publish the 802.3 standard in 1985  Many technologies have challenged Ethernets dominance. However Ethernet has continued to be the dominate LAN product ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 3
  4. 4. Physical and Data Link Features of Ethernet  Standards and Implementation for Ethernet include 802.2 and 802.3 both defined by the IEEE ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 4
  5. 5. Physical and Data Link Features of Ethernet  Ethernet operates across two layers of the OSI model ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 5
  6. 6. Physical and Data Link Features of Ethernet  Logic Link Control – Connecting the Upper Layers ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 6
  7. 7. Physical and Data Link Features of Ethernet  Media Access Control (MAC) ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 7
  8. 8. Ethernet – media changes  Ethernet went from Bus type Coaxial based cable to Star based UTP/STP cables Coaxial Thicknet, (10Base5) Thinet(10Base2) CSMA then CSMA/CD Low Bandwidth Difficult to scale UTP (10Base-T) UTP (100Base-TX) Fiber(100Base –FX) CSMA/CD Higher Bandwidth Scalable ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 8
  9. 9. Ethernet Hubs versus Switches in a LAN.  Legacy Ethernet – Using Hubs suffered multiple collisions Hubs not intelligent devices, Bandwidth is shared, not dedicated per host ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 9
  10. 10. Ethernet – media changes  The movement of Hub based LANs to switched based Ethernet LANs reduced the size of collision domains and improved network availability Multi-port Bridge Intelligent deviceforwards frames based on MAC address Reduce the size of collision domains Increased Bandwidth Communication channel inside switch is dedicated Can support Virtual LANs ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 10
  11. 11. Ethernet Switches versus Hubs in a LAN.  Ethernet – Using Switches ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 11
  12. 12. Ethernet Switches versus Hubs in a LAN.  A switch can eliminate collisions, backoffs and retransmissions, the leading factors in reduced throughput on a hub-based Ethernet network ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 12
  13. 13. Switch operations  Switches forward frames based on their destination MAC addresses. To accomplish their purpose switches use:  Learning (Populate MAC address table with MAC addresses of connected hosts)  Aging (Removes old MAC addresses from table, 5 mins)  Flooding (If a destination entry is not found in the MAC address table that matches the destination in the received frame, the switch floods the frame out all its ports except the port on which the frame entered the switch)  Selective forwarding (Forwarding a frame based on its destination MAC address)  Filtering (Un-forwarded frames based on failed CRC and Port security) ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 13
  14. 14. Physical and Data Link Features of Ethernet  Physical Implementations of the Ethernet ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 14
  15. 15. Ethernet – media changes  High bandwidth Ethernet cabling is used to connect MANS and WAN ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 15
  16. 16. Ethernet Media Access Control Method  CSMA/CD ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 16
  17. 17. Carrier Sense Multiple Access with Collision Detection  Listen before sending – if a device has data to send it must listen for the carrier before sending, if the carrier is detected it must wait a specified time before transmitting  Detecting a collision - If two devices or more fail to detect the carrier they will transmit at the same time. Their data will propagate across the media until a collision occurs, destroying the data. Any device detecting a collision will then transmit a Jam signal  Jam and Random Backoff - Other devices detect the Jam signal and invoke a back off signal for a random amount of time allowing the original collision to subside ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 18
  18. 18. Ethernet Delay (Latency, Bit time, Slot time)  Ethernet data bits don’t move in zero time  Data passing through devices experience delay, can result in collision because the receiving device transmits because it doesn’t see the frame  Bit Time = time for 1 bit to be sensed and placed on the media  Slot time determines Min size of Frame and Max media length ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 19
  19. 19. Ethernet and IEEE frame fields  The IEEE included the extra field (Start of Frame) to allow for extra frame size to accommodate the frames used in switching technology i.e. frames that carry a VLAN field ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 20
  20. 20. Layer 2 addressing is used to identify hosts  The Ethernet MAC Address ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 21
  21. 21. Layer 2 addressing uses Hexadecimal  MAC addresses use Hexadecimal Numbering ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 22
  22. 22. Layer 2 MAC addressing  MAC addressing is used in LANs ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 23
  23. 23. MAC addresses 48 bits or 12 Hex digits  Ethernet Unicast, Multicast and Broadcast  First 6 hex digits OUI + 6 hex digits serial number Organizational Unique Identifier (OUI) ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 24
  24. 24. MAC Address communication types  Unicast – A unique frame sent form a single source to a single destination  Multicast – sent from a single host to a group (or set) of host a LAN segment. Multicast MAC addresses begin with 01-00-5E (Consumes Bandwidth)  Broadcast – sent from a single host to all hosts on the local segment or LAN on Ethernet networks the broadcast address is FF-FF-FF-FF-FF-FF in hexadecimal or 48 1’s in binary (Consumes more Bandwidth) ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 25
  25. 25. Address Resolution Protocol (ARP) process.  Mapping IP to MAC Addresses required to build all frames before frame is converted to bits and placed onto media ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 26
  26. 26. Address Resolution Protocol (ARP) process.  ARP – Destinations Outside the Local Network ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 27
  27. 27. Address Resolution Protocol (ARP) process.  ARP – Removing Address Mappings  When hosts are no longer available mappings have to aged out ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 28
  28. 28. Address Resolution Protocol (ARP) process.  ARP Broadcasts are issued if mapping is not in table ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 29
  29. 29. ARP - process  ARP table maps Destination IP to MAC addresses  Can be populated Dynamically by sensing devices on network or via ARP request (Broadcasts)  Can be populated Statically not recommended as entries don’t age out  To build a Frame the table is first consulted if an entry is not found the source issues an ARP broadcast.  If the destination IP is on a different network an ARP request is sent to determine the MAC address of the gateway ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 30
  30. 30. Labs  9.8.1- Address Resolution Protocol- ARP (ARP command using Wireshark to examine ARP exchanges) ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 31

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