Network+ 1.1 & 1.5 & 1.6

Question 1

What does OSI model stand for?

Answer 1

OSI Model - Open Systems Interconnection Reference Model

Question 2

How many layers are in OSI model?
Name all of them.
Also, say a sentence that is used as a “hint” to remember the layers.

Answer 2

There are 7 layers in the OSI model. 
Layer 1 - Physical
Layer 2 - Data Link
Layer 3 - Network
Layer 4 - Transport
Layer 5 - Session
Layer 6 - Presentation
Layer 7 - Application

7 -> 1 “All People Seem To Need Data Processing” A P S T N D P
Application, Presentation, Session, Transport, Network, Data Link, Physical

Question 3

What is a Layer 1 (physical) for?

Answer 3

Layer 1 - Physical - for Cables, fiber, and the signal itself - electrical signals

Phyisical topology.

Moves bits between devices.
Specifies voltage, wire speed, and pin-out of cables.

“You have a physical layer problem”

• Fix cabling, punch-downs, etc.
• Run loopback tests, test/replace cables, swap adapter cards

Question 4

What is a Layer 2 (Data Link Layer)?

Answer 4

Layer 2 - Data Link Layer or “the switching layer” - Ethernet - Frame, MAC Address, Extended Unique Identified (EUO-48, EUI-64), Switch

Combines packets into bytes and bytes into frames.
Provides access to media using MAC address.
Performs error detection, not correction.

The foundation of communication at the data link.
Data Link Control (DLC) protocols - MAC (Media Access Control) address on Ethernet

Question 5

What is a Layer 3 (Network Layer)?

Answer 5

Layer 3 - Network Layer or the “routing layer” - Network: IP encapsulation - for IP Address, Router, Packet

Routing.
Provides logical addressing, which routers use for path determination.

Internet Protocol (IP)
Fragments frames to traverse different networks.

Question 6

What is a Layer 4 (Transport Layer)?

Answer 6

Layer 4 - Transport Layer - TCP encapsulation - for TCP segment, UDP datagram

End-to-end connection.
Provides reliable or unreliable delivery.
Performs error correction before retransmit.

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol)

Question 7

What is a Layer 5 (Session Layer)?

Answer 7

Layer 5 - Session Layer - Link the presentation to the transport

Dialog control.
Keeps different applications’ data separate.

Communicating management between devices (Start, stop, restart)
Control Protocols, tunneling protocols

Question 8

What is a Layer 6 (Presentation Layer)?

Answer 8

Layer 6 - Presentation Layer - SSL encryption - for application encryption (SSL/TLS)

Data encryption, compression, and translation services.
Presents data.
Handles processing such as encryption.

Character encoding
Application encryption
Often combined with the Application Layer

Question 9

What is a Layer 7 (Application layer)?

Answer 9

Layer 7 - Application Layer - https://mail.google.com - for your EYES

File, print, message, database, and application services.
Provides a user interface.

The layer we see.
HTTP, FTP, DNS, POP3

Question 10

What is encapsulation?

Answer 10

Encapsulation is the process of encoding data as it goes down the Open Systems Interconnection (OSI) stack.

Question 11

What is the central purpose of the OSI model?

Answer 11

Like all networking models, the purpose of OSI model is to allow different vendors’ networks to interoperate smoothly.

Question 12

What are mnemonics to remember the OSI model?

Answer 12

Please Do Not THrow Sausage Pizza Away - Physical, Data Link, Network, Transport, Session, Presentation, Application

All People Seem To Need Data Processing - Application Presentation Session Transport Network DataLink Physical

Question 13

Does the upper layer know anything about network addresses?

Answer 13

No.

The upper layers (5 - 7) (Session, Presentation, Application) don’t know anything about networking or network addresses.

Question 14

What does the bottom 4 layer know about networking or data?

Answer 14

It’s the responsibility of the bottom 4 layers to know networking and networking addresses.

These bottom layers determine how to rebuild a data stream from a transmitting host to a destination hosts’s application.

Question 15

How do users communicate on the application layer?

Answer 15

API - Application Programming Interfaces

APplication processes, interfaces.

Question 16

What is a virtual circuit? Is it called connection-oriented or connectionless?

Answer 16

When the sender’s TCP process contacts the destination’s TCP process to establish a connection, the resulting creation is called “a virtual circuit”.

This type of communication is connection-oriented.

After all of this required synchronization occurs, a connection is fully established and the data transfer begins. This virtual circuit setup is called overhead.

Question 17

Describe the steps of the TCP three-way handshake:

Answer 17

In simple words: SYN, SYN/ACK, ACK.

1. The first “connection agreement” segment is a request for synchronization.
2. The next segments acknowledge the request and establish connection parameters - the rules - between hosts. These segments request that the receiver’s sequencing is synchronized here as well so that a bidirectional connection is formed.
3. The final segment is also an acknowledgment. It notifies the host that the connection agreement has been accepted and that the connection has been established. Data transfer can now begin.

Question 18

What is a router? What layer does it use?

Answer 18

Routers are layer 3 devices that are specified at the Network layer and provide the routing services within the internetwork.

Question 19

What is a Data Link layer (2) responsible for?

Answer 19

The Data Link layer (2) is responsible for the unique identification of each device that resides on a local network.

Question 20

What does LLC stand for?

Answer 20

LLC - Logical Link Control

In the IEEE 802 reference model computer networking, the logical link control data communication protocol layer is the upper sublayer of the data link layer of the seven-layer OSI models.

LLC sublayer acts as an interface between the media access control sublayer and the network layer.

Question 21

What is an encapsulation order?

Answer 21

Data, segment, packet, frame, bits.

Question 22

What does CSMA/CD stand for and which IEEE standard specifies the protocol for it?

Answer 22

The 802.3 standard, commonly associated with Ethernet specifies the media-access method used by Ethernet, which is known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

Question 23

What does FQDN stand for?

Answer 23

FQDN stands for Fully Qualified Domain Name.

It includes all the components from the top of DNS Namespace to the host.