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53: Introduction

https://www.udemy.com/cisco-icnd1/learn/lecture/8601360#content

54: Local Are Network Layer 2 – Ethernet

https://www.udemy.com/cisco-icnd1/learn/lecture/8601364#content

• Frames are encoded and decoded into bits at Layer 2
• Error detection and correction for the physical layer can be provided here.
• Ethernet is the Layer 2 medium used on Local Area Networks
• https://en.wikipedia.org/wiki/List_of_network_protocols_(OSI_model)

OSI Reference Model – Encapsulation

• Layer 7 (Application): Data
• Layer 6 (Presentation)
• Layer 5 (Session)
• Layer 4 (Transport): Segment
• Layer 3 (Network): Packet
• Layer 2 (Data-Link): Frame
• Layer 1 (Physical)

The Ethernet Header

• Preamble: 8 Bytes
  • Used to help the sender and receiver synchronize
• Destination and Source Addresses: 6 Bytes each
  • MAC addresses
• Length/EtherType: 2 Bytes
  • Describes what is encapsulated in the Header
  • Usually IPv4
• Data: 46 – 1500 Bytes
• FCS (Frame Check Sequence): 4 Bytes
  • aka Redundancy check
  • Used to check the integrity of the frame to ensure there hasn’t been any corruption.

The Media Access Control (MAC) Address

• Ethernet uses a 48 bit hexidecimal MAC Address
• The first 24 bits is the OUI (Organizationally Unique Identifier) which identifies the manufacturer of the Ethernet Port.
  • The OUI is assigned by the IEEE
• The last 24 bits are vendor assigned.
• The burned in MAC address on every NIC port in the world is globally unique
  • Example: 00:50:56:C0:00:08

How to find your MAC Address

• Windows:
  • ipconfig /all
• Linux:
  • ifconfig
• Cisco Route
  • #show interface
  • BIA = Burned In Address