Ethernet

Ethernet

1. Ethernet encapsulation

   • Sublayer LLC
   • MAC sublayer
     • Data encapsulation
       • Frame delimitation
       • Addressing
       • Error detection
     • Media access control

2. Ethernet frame fields

   • Preamble
     • Frame Start Delimiter
   • destination mac address
     • identifier field of the desired destination
   • source mac address
     • This 6-byte field identifies the NIC or the source interface of the frame. It must be a unicast address.
   • EtherType field
     • This 2-byte field identifies the upper layer protocol encapsulated in the Ethernet frame. Common values ​​are, in hexadecimal, "0x800" for IPv4, "0x86DD" for IPv6 and "0x806" for ARP.
   • Data field
     • It contains the encapsulated data of an upper layer, which is a Layer 3 PDU or, more commonly, an IPv4 packet.
   • Frame check sequence field
     • The Frame Verification Sequence (FCS) field (4 bytes) is used to detect errors in the frame.

3. MAC and hexadecimal address

   • Decimal
   • Binario
   • Hexadecimal

4. MAC Address: Ethernet Identity

   • MAC address structure
     • MAC is the direct result of the standards implemented by the IEEE for providers with the aim of guaranteeing unique addresses for each Ethernet device.

5. MAC address representations

   • View
     • ipconfig /all
     • ipconfig

6. Unicast MAC Address

   • is the unique address used when a frame is sent from a single transmitter device to a single receiving device.

7. MAC broadcast address

   • Broadcast packets have a destination IPv4 address that contains only numbers one (1) in the host portion.

8. Multicast MAC Address

   • Multicasting allows a source device to send a packet to a group of devices. A multicast group IP address is assigned to devices that belong to a multicast group.

9. Basic notions of switches

   • A layer 2 Ethernet switch uses MAC addresses to make forwarding decisions.

10. Obtaining MAC Addresses

    • switch
      • MAC address table dynamically
        • after examining the source MAC address of the frames received on a port

11. Frame Filtering

    • When the switch MAC address table contains the destination MAC address

12. Switching by cutting method

    • Fast forwarding switching
    • Fragment free switching

13. Buffering memory on switches

    • Port-based memory buffer
    • Shared memory buffer

14. Duplex and speed settings

    • Full duplex
    • Half duplex
    • Duplex Incompatibility

15. MDIX automatic

    • most switch devices allow the mdix auto interface configuration command in the CLI to activate the automatic medium-dependent cross-interface (MDIX) function

16. Destination on the same network

    • Physical address (MAC address)
      • NIC Ethernet communications to NIC Ethernet on the same network.
    • Logical address (IP address)
      • send the package from the initial origin to the final destination.
    • Destination MAC address
      • is the MAC address of the Ethernet NIC of the file server.
    • Source MAC address
      • is the MAC address of the Ethernet NIC of PC-A.

17. Destination remote network

    • the destination MAC address is the host default gateway address

18. Introduction to ARP

    • Destination MAC address
      • It is the address of the final destination or router.
    • Source MAC address
      • the MAC address of the sender's Ethernet NIC.

19. Deleting entries from an ARP table

    • ARP cache deletes ARP entries that have not been used for a specified period

20. ARP broadcasts

    • All devices on the local network receive and process an ARP request because it is a broadcast frame

21. ARP impersonation

    • In some cases, the use of ARP can cause a potential safety risk known as "ARP impersonation" or "ARP poisoning."