Transport layer

Question 1

What’s the biggest difference between network layer and transport layer? (3rd and 4th layers in OSI model)

Answer 1

Transport layer provides point to point connectivity while the network layer is only responsible for forwarding the data from one device to the next

Question 2

Name transport layer protocols.

Answer 2

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

Question 3

What are the steps in a TCP three-way handshake?

Answer 3

Device A wants to establish a connection. It sends a SYN (Synchronize sequence number) to device B, which replies with SYN+ACK (Acknowledgment). then Device A sends ACK to B.

Question 4

If data is in frames on data link layer, packets on network layer, what are they called on transport layer?

Answer 4

segments

Question 5

What is a combination of IP address+port number sometimes called?

Answer 5

a socket

Question 6

What’s the difference between system ports and user ports?

Answer 6

starting a service in system ports (0-1023) require admin priviledges, while in user ports (1024-49151) it doesn’t

Question 7

What are ports for HTTP, HTTPS and SSH

Answer 7

80, 443, 22 respectively

Question 8

Name the important parts of a TCP header:

Answer 8

source port, destination port, sequence number, acknowledgement number, window size, checksum

Question 9

What is UDP used for?

Answer 9

Applications that can withstand some packet loss but require low latency, such as video and sound streaming.

Question 10

Why is TCP used over UDP in many cases?

Answer 10

TCP is reliable data transfer (but bit slower)

Question 11

Is DNS TCP or UDP?

Answer 11

UDP

Question 12

How can a web server identify different established sessions?

Answer 12

By IP+port number (There can be many sessions from same IP)