Ethernet

Ethernet

1. Ethernet Encapsulation

   • Ethernet supports data bandwidths of
     • 10 Mb/s
     • 100 Mb/s
     • 1000 Mb/s (1 Gb/s)
     • 10 000 Mb/s (10 Gb/s)
     • 40 000 Mb/s (40 Gb/s
     • 100 000 Mb/s (100 Gb/s)
   • LLC sublayer
     • The Ethernet LLC sublayer handles the communication between the upper layers and the lower layers.
   • MAC sublayer
     • MAC constitutes the lower sublayer of the data link layer.

2. MAC Sublayer

   • Data encapsulation
     • Frame delimiting
     • Adressing
     • Error detection
   • Media Access Control
     • Control of frame placement on and off the media
     • Media Recovery

3. Ethernet Evolution

   • Since the creation of Ethernet in 1973, standards have evolved for specifying faster and more flexible versions of the technology.

4. Ethernet Frame Fields

   • Preamble
   • Destination MAC address
   • Source MAC address
   • EtherType
   • Data
   • FCS

5. MAC Address and Hexadecimal

   • An Ethernet MAC address is a 48-bit binary value expressed as 12 hexadecimal digits (4 bits per hexadecimal digit).

6. Unicast MAC Address

   • In Ethernet, different MAC addresses are used for Layer 2 unicast, broadcast, and multicast communications.
     • Unicast
       • A unicast MAC address is the unique address used when a frame is sent from a single transmitting device to a single destination device.

7. Broadcast MAC Address

   • A broadcast packet contains a destination IPv4 address that has all ones (1s) in the host portion.
     • Broadcast
       • This numbering in the address means that all hosts on that local network (broadcast domain) will receive and process the packet.

8. Multicast MAC Address

   • Multicast addresses allow a source device to send a packet to a group of devices.

9. Filtering Frames

   • As a switch receives frames from different devices, it is able to populate its MAC address table by examining the source MAC address of every frame.
     • When the switch’s MAC address table contains the destination MAC address, it is able to filter the frame and forward out a single port.

10. Frame Forwarding Methods on Cisco Switches

    • Store-and-forward switching
      • A store-and-forward switch receives the entire frame, and computes the CRC.
    • Cut-through switching
      • A cut-through switch forwards the frame before it is entirely received.

11. Cut-Through Switching

    • A cut-through switch forwards the frame before it is entirely received.

12. Memory Buffering on Switches

    • Port-based Memory Buffering
      • In port-based memory buffering, frames are stored in queues that are linked to specific incoming and outgoing ports.
    • Shared Memory Buffering
      • Shared memory buffering deposits all frames into a common memory buffer that all the ports on the switch share.

13. Duplex and Speed Settings

    • Full-duplex
      • Both ends of the connection can send and receive simultaneously.
    • Half-duplex
      • Only one end of the connection can send at a time.

14. Auto-MDIX

    • MDIX auto detects the type of connection required and configures the interface accordingly.

15. Destination on Same Network

    • Physical address (the MAC address)
      • Used for Ethernet NIC to Ethernet NIC communications on the same network.
    • Logical address (the IP address)
      • Used to send the packet from the original source to the final destination.

16. Introduction to ARP

    • Destination MAC address
      • The MAC address of the Ethernet NIC, which will be either the MAC address of the final destination device or the router.
    • Source MAC address
      • The MAC address of the sender’s Ethernet NIC.

17. ARP Functions

    • When a packet is sent to the data link layer to be encapsulated into an Ethernet frame, the device refers to a table in its memory to find the MAC address that is mapped to the IPv4 address.

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