Networks

Question 1

What is a network?

Answer 1

A connection between at least two nodes through a communication link

Question 2

Network edge

Answer 2

End nodes (like client and server)

Question 3

Network core

Answer 3

Interconnecting devices (like switch, hub, router)

Question 4

Define hub

Answer 4

Interconnecting device. Whatever messages come in one port are sent to all other ports, does NOT allow direct device to device communication. Uses broadcast messages only. Looks at MAC address only.

Question 5

Define switch

Answer 5

Interconnecting device. A smart hub. Keeps track of which devices are on which ports and only sends messages to the right ports. Device to device communication. Uses unicast messages. Looks at MAC address only.

Question 6

Router

Answer 6

Interconnecting device. Uses IP addresses.

Question 7

Port

Answer 7

Logical construct that identifies a specific process of the type of network service

Question 8

Does the port number need to be unique within a device? Does it need to be unique BETWEEN devices?

Answer 8

Yes (same building, diff apt #)
No (diff building, same apt #)

Question 9

Common port numbers

Answer 9

HTTP: 80
HTTPS: 443
SMTP: 25
FTP: 21
DNS: 53
DHCP -> Client: 68, Server: 67
SSH: 22
Telnet: 23

Question 10

OSI Model

Answer 10

7. Application - enables user to access the network of the internet resources (browser, email, etc)
8. Presentation - encoding, encryption, data compression. computer language is binary so conversion happens here.
9. Session- it’s in charge of establishing and terminating the communication session
10. Transport - provides end to end, host to host, process to process communication
11. Network - sends data over multiple networks using the IP address
12. Data Link - responsible for moving data from one node to the next one
13. Physical - where the encoding and decoding process will be performed

Question 11

How are encoding in physical layer and encoding in presentation layer different in OSI Model?

Answer 11

In presentation, you convert from regular to binary language. In physical, we convert from binary to signals and vice versa.

Question 12

5. Application Layer - TCP/IP Model

Answer 12

Enables user to access the internet resources.

Main protocols: FTP (file transfer), SSH/telnet (remote access), HTTP (hypertext transfer protocol), HTTPs (secure), SMTP (email), DNS (map domain name to IP address), DHCP (assigns IP addresses to the hosts/machines)

Question 13

4. Transport Layer - TCP/IP Model

Answer 13

Provides end to end, host to host, process to process delivery of the message.

Functions: Port addressing, segmentation and reassembly, connection control.

Connection oriented - error control, flow control, congression control

Question 14

Network Layer - TCP/IP Model

Answer 14

Sending the messages over multiple networks using the IP addresses of the source machine and the destination machine

Functions: Logical addressing (IP address) and routing (finding the best route from source to destination)

Versions of IP
IPv4 - 32 bits, 4 Bytes.
IPv6 - 16 Bytes

Private IP vs Public IP

Question 15

Data Link Layer - TCP/IP Model

Answer 15

Responsible for moving data from one node to the next node. Link to link.

Main functions: framing and physical addressing. Physical addressing assigns the MAC (physical) address to the message.

-MAC address is a hard coded address on the network card. It’s fixed. 6 Bytes.

IP address will be changed all the time.

Question 16

Physical Layer - TCP/IP Model

Question 17

If we are using the OSI model, the encryption will be in presentation layer. If we use TCP/IP, where will encryption be performed?

Answer 17

Application layer

Question 18

Difference between Private IP and Public IP

Answer 18

Private - for local networks or small offices, NOT ROUTABLE, we cannot use it on internet. Private IP MUST BE UNIQUE WITHIN THE PRIVATE NETWORK ONLY. They do not need to be unique BETWEEN private networks. There is a specific range of IPs that can be used as private IPs only, like 10.10.10 and 192.68.

Public - for public networks and all devices on internet, ROUTABLE, we can use it on the internet

All the private IP addresses in the private network will be mapped to one public IP

Question 19

When you’re at home and the computer is assigned to a private IP, do you have any issue accessing the internet?

Answer 19

The network address translator (NAT) will replace the private IP with a public IP to allow user to access the internet.

Question 20

What do we use the MAC address for?

Answer 20

We use the MAC address for the device to communicate over the local network.

Question 21

IP Address vs MAC Address vs Port Number

Answer 21

IP Address: reach the destination network (network layer)

MAC Address: reach the correct device on the network (data link layer)

Port number: reach the correct process within the device (transport layer)

Question 22

What is the difference between TCP and UDP?

Answer 22

TCP: Reliable & connection oriented. Receiver must acknowledge receiving the message. Three way handshake where the sender and receiver must establish a connection before exchanging data. HTTP, HTTPS, FTP, SMTP, SSH, TELNET use this.

UDP: unreliable and connectionless. No acknowledgement sent back. Speedy. DNS and DHCP use it.