TCP

Question 1

What is TCP?

Answer 1

Protocol that control transmission

Question 2

What are some TCP use cases ?

Answer 2

1. Database connection
2. Web connection
3. Remote ssh connection
4. Any bidirectional communication

Question 3

How segments are being tracked in TCP ?

Answer 3

They are numbered with a sequence and acknowledge for “ order and retransmission purposes”

Question 4

What is a file descriptor ?

Answer 4

Everything in linux is treated as a file , tcp connection is called file descriptor that uniquely represent a socket.

Socket/file descriptor example :
10.0.0.1:5555:10.0.0.2:22

Question 5

What is a Four way handshake ?

Answer 5

The way a TCP connection is closed (fin-ack-fin-ack) , we delete the file descriptors from both sides

Question 6

What is flow control ?

Answer 6

Property of TCP which manage how much a receiver can handle

Question 7

What are the components of flow control ?

Answer 7

1. Receiver window
2. Sliding window (when the sender receives as acknowledgment it will slide its window

Question 8

What is congestion control ?

Answer 8

A way to avoid congestion the middle boxes (routers) between receiver and sender

Question 9

What are the existing algorithms of congestion control ?

Answer 9

1. Slow start : with each ack , increment the MSS (maximum segment size) by one
2. Congestion avoidance : increases linearly , all sent segments needs to be acknowledged to increase the MSS

Question 10

How can the router notify the sender that it will face a congestion ?

Answer 10

Every IP header have an ECN (explicit congestion notification) flag which the router will set to 1 if its facing a congestion

Question 11

How the router remember the ips when doing NAT ?

Answer 11

He keeps a NAT Table of the ips he replaced