Section 3: OSI Model

Question 1

What is the Open Systems Interconnection model (OSI)?

Answer 1

A reference model for troubleshooting networks

Question 2

What are the OSI model layers from top to bottom?

Answer 2

7) Application
6) Presentation
5) Session
4) Transport
3) Network
2) Data Link
1) Physical

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Question 3

What are the data types in the OSI model?

Answer 3

• Application, Presentation, Session: Data
• Transport: Segments
• Network: Packets
• Data Link: Frames
• Physical: Bits

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Question 4

What is the physical layer (Layer 1)?

Answer 4

Transmission of bits across the network

Question 5

What is considered standard wiring for RJ-45 cables and ports?

Answer 5

TIA/EIA-568-B

Question 6

What do crossover cables use? (List 2)

Answer 6

T-568A & T-568B

Question 7

What is broadband bandwidth? List an example

Answer 7

Divides bandwidth into separate channels

Cable TV

Question 8

What is baseband bandwidth? List an example

Answer 8

Uses all available frequency on a medium (cable) to transmit data and uses a reference clock to coordinate the transmissions by both sender and receiver

Ethernet

Question 9

What are some examples of Layer 1 of the OSI Model? List at least 3

Answer 9

Ethernet, Fiber Optic, Wi-Fi, Bluetooth, WAPs, Hubs

Question 10

What is the data link layer (Layer 2)?

Answer 10

Packages data into frames and transmitting those frames on the network, performing error detection/correction, and uniquely identifying network devices with an address, and flow control.

Question 11

What is a media access control (MAC) address?

Answer 11

A 48-bit physical address assigned to a network interface card (NIC) by manufacturer

Question 12

What is flow control?

Answer 12

Limits amount of data sender can send at one time to keep receiver from becoming overwhelmed

Question 13

What are some examples of Layer 2 of the OSI Model? List at least 3

Answer 13

NICs, Bridges, Switches

Question 14

What is the network layer (Layer 3)?

Answer 14

Forwards routing traffic with logical address

Question 15

What are the two Internet Protocols (IPs)?

Answer 15

IPv4 & IPv6

Question 16

What is internet control message protocol (ICMP)?

Answer 16

Used to send error messages and operational information about an IP destination

Used in troubleshooting (ping & traceroute)

Question 17

What are some example of Layer 3? List at least 3

Answer 17

Routers, Multilayer Switches, IPv4, IPv6, ICMP

Question 18

What is the transport layer (Layer 4)?

Answer 18

Connection-oriented protocol that is a reliable way to transport segments across the network

Data is sent in segments

Question 19

What is transmission control protocol (TCP)?

Answer 19

A connection-oriented protocol

A reliable transport of segments

Question 20

What is user datagram protocol (UDP)?

Answer 20

A connectionless protocol

An unreliable transport of segments

Question 21

What are some examples of Layer 4? List at least 3

Answer 21

TCP, UDP, WAN Accelerators, Firewalls, Load Balancers

Question 22

What is a session layer (Layer 5)?

Answer 22

Keeps conversations separate to prevent intermingling of the data

Question 23

What are some examples of Layer 5?

Answer 23

H.323 & NetBIOS

Question 24

What is the presentation layer (Layer 6)?

Answer 24

Formats the data exchanged and securing that data with proper encryption

Question 25

What is **encryption**?

Answer 25

Used to scramble the data in transit to keep it secure from prying eyes | Provides confidentiality of data

Question 26

What are some examples of Layer 6? List at least 3

Answer 26

HTML, XML, UNICODE, ASCII, GIF, JPG, TLS, SSL

Question 27

What is the **application** layer (Layer 7)?

Answer 27

Provides services where users communicate with the computer

Question 28

What are some examples of Layer 7? List at least 3

Answer 28

Email, Web Browsing, Remote Access, Domain Name Service, File Transfer Protocol

Question 29

What is **encapsulation**?

Answer 29

The process of putting headers (and sometimes trailers) around some data | Move down the OSI layers from 7 to 1, we encapsulate

Question 30

What is **decapsulation**?

Answer 30

Action of removing the encapsulation that was applied | Move up from layers 1 to 7, we decapsulate data

Question 31

What is the **SYN (Synchronous) Flag**?

Answer 31

The most well-known flag in TCP communications because it is used to synchronize the connection during the three-way handshake

Question 32

What is the **ACK (Acknowledgement)** flag?

Answer 32

Used during the three-way handshake, but is also used to acknowledge the successful receipt of packets

Question 33

What is the **FIN (Finished)** packet?

Answer 33

Used to tear down virtual connections created using the three-way handshake and the SYN flag | Appears when the last pakets are exchanged between a client and server

Question 34

What is the **RST (Reset)** flag?

Answer 34

Used when a client or server receives a packet that it was not expecting during the current connection

Question 35

What is a **PSH (PUSH)** flag?

Answer 35

Used to ensure that the data is given priority and is processed at the sending or receiving ends

Question 36

What is the **URG (Urgent)** flag?

Answer 36

Like the PUSH flag and identifies incoming data as "urgent" | Sent to tell the recipient to process it immediately and ignore others