1.1 Ports and Protocols

Question 1

What is the ICMP protocol type?

Answer 1

answers “is there a computer with this IP?” at the internet layer of the IP stack

ping is an application that runs under ICMP. It will show RTT (round trip time) for the ICMP packet in seconds.

Unlike TCP and UDP, this is a same layer protocol but no data is transmitted. It is a control protocol

Question 2

WHAT ARE THE INTERNET LAYER PROTOCOLS

Answer 2

IPv4
IPv6
ICMP

Question 3

What does the internet layer do?

Answer 3

takes data chunks from the transport layer, adds addressing, creates the final IP packet. then it gives it to layer 2 to be encapsulated into a frame.

Question 4

WHAT ARE THE TRANSPORT LAYER PROTOCOLS?

Answer 4

TCP
UDP

ICMP is transport or network layer (no consensus)

Question 5

What does the transport layer do?

Answer 5

Is the communication connection-oriented or connectionless?

connection oriented matters for:
- arriving in the right order
- secure
- slower

connectionless
- doesn’t care if some bits are missing
- fast

95% of app protocols use TCP

Question 6

Explain TCP

Answer 6

• uses ACK/NACK for the process of knowing if two machines are ready to send and receive data
• chops data into segments
• give segments a sequence number
• verify that all sent segments are received
• request missing segment if not received

source port listed first, then dest port

Question 7

TCP header fields

Answer 7

• source port (FIRST)
• destination port
• sequence number
• ACK numbers
• flags
• checksum

Question 8

WHAT ARE THE APPLICATION LAYER PROTOCOLS?

Question 9

What is the TCP protocol type?

Answer 9

Transmission Control Protocol. A connection-oriented protocol.

95% of apps use TCP, which is why we call it the TCP/IP stack and not UDP/IP.

Question 10

What is the UDP protocol type?

Answer 10

User Datagram Protocol. A connectionless protocol.

Use when there’s a lot of data that doesn’t need to be perfect or the systems are extremely close to each other and unlikely to have transmission issues.

VoIP calls can afford to drop some frames

It’s FAST

Question 11

2 famous UDP protocols

Answer 11

DNS and DHCP

Question 12

how many fields are in an IP packet?

Answer 12

14

Question 13

What are the fields in the IP packet?

Answer 13

version: IPv4 or IPv6?
header length: e.g. 32 bits
DSCP differentiated services code point: data used by bandwidth sensitive apps like VoIP
TTL Time To Live: TTL prevents an IP packet from infinitely looping if there are issues.
protocol: nearly always TCP or UDP and IDs what’s inside the packet