OSI Layer 2 - Data-Link Layer

Question 1

Layer 2 Overview

Answer 1

Frames are encoded/decoded into bits at Layer 2

Error detection & correction for the Physical layer can be provided here

Ethernet is the Layer 2 medium used on LANs

Question 2

Ethernet Header

Answer 2

Preamble - 7 bytes
Destination Address - 6 bytes
Source Address - 6 bytes
Length/Ethertype - 2 Bytes
Data - (Variable) 46-1500 bytes
FCS (Frame Check Sequence) - 4 bytes

Question 3

Preamble Function

Answer 3

Helps the sender & receiver to synchronize

Question 4

Term for the message in Layer 2

Answer 4

Frame

Question 5

FCS

Answer 5

Frame Check Sequence:

A cyclical redundancy check which is used to check for the integrity of the frame
To check that it has not been corrupted during transit

Question 6

OUI

Answer 6

Organizationally Unique Identifier:

First 24 bits of a MAC Address
Assigned by IEEE

Question 7

Ethertype

Answer 7

Used to specify what is encapsulated inside the Ethernet header

Question 8

MAC Address

Answer 8

Media Access Control Address:
48 bits (6 bytes)
Hexadecimal
First 24 bits = OUI
Last 24 bits = Vendor assigned