1. Network Models

Question 1

OSI Layer 7

Answer 1

Application

User-facing software that is being used to engage with a network. Could be anything from LAN file sharing to a browser. APIs provide service to the programs that the users see.

PDU: data

Question 2

OSI Layer 6

Answer 2

Presentation

Translates data from the lower layers into formats usable by applications, and vice versa. This is where encryption happens.

PDU: data

Question 3

OSI Layer 5

Answer 3

Session

Handles the process of differentiating between various types of connections on a PC. This layer initiates sessions, accepts incoming sessions, and opens and closes existing sessions.

PDU: data

Question 4

OSI Layer 4

Answer 4

Transportation

This is where data is ‘packetized’ into sections that can be passed individually through a network. Data is broken up and sequence numbers for TCP segments are added so the receiving computer can assemble correctly.

PDU: segment

Question 5

OSI Layer 3

Answer 5

Network

Creates and addresses packets. The IP addressing enables routers to make sure the packets get to the correct system without worrying about the type of hardware used for transmission.

Device: Router
PDU: packet

Question 6

OSI Layer 2

Answer 6

Data Link

The only layer with sublayers. Home of the NIC. Puts the final frame on the data before getting passed through the network.

Device: Switch
PDU: frame

Question 7

OSI Layer 1

Answer 7

Physical

Any medium on which data travels, even radio waves.

Devices: cables, hubs
PDU: bit

Question 8

LLC

Answer 8

Logical Link Control

Sublayer of the Data Link Layer 2. Handles multiple network protocols and provides flow control.

Question 9

MAC

Answer 9

Media Access Control

Sublayer of Data Link Layer 2. It adds the NIC’s own MAC address and attaches MAX addresses to the frames and adds or checks the FCS.

The number is represented in hexadecimal and it split into 2 parts. The first being the Organizationally Unique Identifier (OUI) and the second being the device ID.

Question 10

FCS

Answer 10

Frame Check Sequence

The resulting remainder of a division problem applied to a frame’s data. Allows the receiving computer to verify all the data was received.

Question 11

NIC

Answer 11

Network Interface Card

Houses the LLC and the MAC

Question 12

TCP/IP Layer 1

Answer 12

Link Layer / Network Interface Layer

Covers the first two layers of the OSI model (switches, frames).

Question 13

TCP/IP Layer 2

Answer 13

Internet Layer

Same as the OSI’s Network Layer. Covers anything involved with IP, including packets, addressing, and routing.

Question 14

TCP/IP Layer 3

Answer 14

Transport Layer

Similar to the OSI Transport layer except that the PDU is either a TCP segment or a UDP datagram, depending on the protocol used. Also, port numbers are added, and in the case of TCP, sequence numbers.

Question 15

TCP/IP Layer 4

Answer 15

Combines the top three OSI layers. The session component works similarly, the presentation doesn’t exist, and connection to an application is implied.

Question 16

API

Answer 16

Application Programming Interface

Provide a standard way for programmers to enhance or extend an applications capabilities.

Question 17

EUI-48

Answer 17

The IEEE’s official term for a MAC address

Question 18

CRC

Answer 18

Cyclic Redundancy Check

aka FCS

Question 19

datagram

Answer 19

The PDU of the UDP (the TCP version would a segment).

Question 20

physical address

Answer 20

Synonymous with the MAC address

Question 21

device ID

Answer 21

The second half of a MAC address.

Question 22

EUI-48

Answer 22

The IEEE’s official term for a MAC address / physical address.

Question 23

frame

Answer 23

The structure in which data gets passed around a network. Contains a header, payload, and trailer.

Question 24

header

Answer 24

First section of a frame, contains the MAC address and data type

Question 25

TCP/IP model

Answer 25

Transmission Control Protocol / Internet Protocol

..

Question 26

IP address

Answer 26

A unique numeric identifier.

aka logical address

Question 27

logical address

Answer 27

aka IP address

Question 28

logical addressing

Answer 28

Refers to digital addressing which can be configured.

Question 29

MAC-48

Answer 29

Synonymous with EUI-48, MAC address, and physical address

Question 30

network protocol

Answer 30

How computers handle addressing large networks

Question 31

payload

Answer 31

The actual data in a frame, excluding the header and any other metadata.

Question 32

packet

Answer 32

The PDU of the Network layer. The packet is inside the frame containing the payload and a separate header. The header contains source address, destination address, protocol, and sequence number.

Question 33

protocol

Answer 33

An agreement between devices defining how they will exchange data.

Question 34

reassembly

Answer 34

The reverse of segmentation. TCP segments are put back together in the proper order.

Question 35

router

Answer 35

A device that routes data to the next point in the network without needing to know its final destination.

Question 36

segment

Answer 36

The PDU of the TCP

Question 37

segmentation

Answer 37

The process of the local computer “packetizing” it’s data into sections that can be passed individually through the network.

Question 38

session software

Answer 38

Connects applications to other applications and ensures that they are compatible.

Question 39

subnet

Answer 39

Technically a division of a network by range of IP address. Represents a subnet of hosts which can be reached over a network interface.

Question 40

TCP segment

Answer 40

TCP accepts a data stream, divides it into sections and adds a TCP header. Thus, a TCP segment is born.

Question 41

trailer

Answer 41

Metadata attached to the end of a