Chapter 1 - OSI Model

Question 1

The OSI Model

Answer 1

Seven layer model where each layer defines an important function in computer networking.
Layer 7- Application
Layer 6- Presentation
Layer 5- Session
Layer 4- Transport
Layer 3- Network
Layer 2- Data Link
Layer 1- Physical

Question 2

Layer 7

Answer 2

Application Layer

Question 3

Layer 6

Answer 3

Presentation Layer

Question 4

Layer 5

Answer 4

Session Layer

Question 5

Layer 4

Answer 5

Transport Layer

Question 6

Layer 3

Answer 6

Network Layer

Question 7

Layer 2

Answer 7

Data Link Layer

Question 8

Layer 1

Answer 8

Physical Layer

Question 9

Physical Layer

Answer 9

Layer 1
Defines the method of moving data between computers. Anything that moves data from one system to another- copper cabling, fiber optics, even radio waves

Question 10

Data Link Layer

Answer 10

Layer 2
Focuses on physical addressing; adds in MAC address of the receiving endpoint
Checks received data to ensure it wasn’t corrupted in transit
NICs and Switches included here

Question 11

Network Layer

Answer 11

Layer 3
Responsible for locating the destination of your request, uses logical addressing (IP addresses)

Question 12

Transport Layer

Answer 12

Layer 4
Selects the protocol to send the data over (TCP or UDP) then divides it into segments or datagrams for transmission

Also does reassembly on the other end

Question 13

Session Layer

Answer 13

Layer 5
Creates and maintains separate sessions between other computers

Question 14

Presentation Layer

Answer 14

Layer 6
Translates the data into a standardized format, as well as handling any encryption, compression or other transformations to the data

Question 15

Application Layer

Answer 15

Layer 7
Provides networking options to programs running on a computer
(APIs)

Question 16

In the Transport Layer, encapsulated data is referred to as ____

Answer 16

Segments or Datagrams depending on whether TCP or UDP is being used

Question 17

At the Network Layer, encapsulated data is referred to as ___

Answer 17

Packets

Question 18

At the Data Link Layer, encapsulated data is referred to as ___

Answer 18

Frames

Question 19

What Layer is the only one to add a trailer in addition to a header?

Answer 19

Data Link

Question 20

NIC

Answer 20

Network Interface Card
Serves as the interface between the PC and the network. Each one has a unique MAC address for identification

Question 21

MAC Address

Answer 21

Unique, 48-bit identifier. No two NICs ever share the same MAC address
Any company that makes NICs must contact IEEE and request a block of MAC addresses

Question 22

MAC-48

Answer 22

Original name for the format assigned to MAC addresses by IEEE. Means the MAC address will be 48 bits, with the first 24 bits defining the OUI

Question 23

OUI

Answer 23

Organizationally Unique Identifier; first 24 bits of MAC address and unique to each manufacturer

Question 24

EUI-48

Answer 24

Current term for format IEEE uses for MAC Addresses.
Extended Unique Identifier
48 bits with first 24 bits being the OUI

Question 25

Frame

Answer 25

Container for discrete chunks of data moving across a network
Operates at Layer 2 and uses MAC addresses

Question 26

FCS

Answer 26

Frame Check Sequence
The trailer for a Frame; this is checked by the receiving NIC to validate that data arrived intact

Question 27

The three sections of a frame

Answer 27

Header- MAC address and Type
Payload- Whatever is encapsulated in the frame
Trailer- FCS

Question 28

Broadcast Address

Answer 28

Layer 2 MAC Address of FF-FF-FF-FF-FF-FF
Used to broadcast out to all NICs on a network to discover the MAC of a specific device

Question 29

Any frame addressed specifically to another device’s MAC address is called a ___

Answer 29

Unicast Frame

Question 30

Logical Link Control (LLC)

Answer 30

Sublayer of Layer 2
Aspect of the NIC that talks to the system’s OS (usually via device drivers). The LLC handles multiple network protocols and provides flow control

Question 31

Media Access Control (MAC)

Answer 31

Sublayer of Layer 2
Creates and addresses the frame
Adds the NICs own MAC address and attaches MAC addresses to the frames
Adds or checks the FCS

Question 32

NICs operate at which layer(s)?

Answer 32

Both Layer 2 and 1 as they handle MAC addressing AND putting the data on the network cable.
If forced to pick between one or the other, the most common answer is layer 2

Question 33

Internet Protocol

Answer 33

Primary logical addressing protocol for TCP/IP
Makes sure that a piece of data gets to where it needs to go on the network by giving each device on the network an IP address

Question 34

Router

Answer 34

Operates at layer 3, connects each subnet and forwards data using IP addresses

Question 35

Encapsulation

Answer 35

The entire process of preparing data to go onto a network
Includes all steps from the application to the following layers where more info is added:
Application
Presentation
Session
Transport
Network
Data Link

Question 36

De-Encapsulation

Answer 36

Reverse of encapsulation where the receiving computer strips away all extra header information

Question 37

TCP

Answer 37

Transmission Control Protocol
Connection-oriented protocol, meaning a verification of a good connection is required, as well as confirmation of receipt

Question 38

UDP

Answer 38

User Datagram Protocol
Connectionless protocol, “fire and forget”

Question 39

TCP segment

Answer 39

Container with fields that ensure data gets to its destination.
Includes source and destination ports, sequence number, checksum, flags, acknowledgement, and the data itself

Question 40

Port

Answer 40

Logical value assigned to specific applications or services