Intro to IP

Question 1

TCP

Answer 1

Transmission Control Protocol

• Connection oriented, has a formal setup and close
• “Reliable” delivery (recovery from errors, can manage out-of-order messages or retransmissions)
• Flow control (the receiver can manage how much data is sent)

Question 2

UDP

Answer 2

User Datagram Protocol

• Connectionless, no formal open/close to the connection
• “Unreliable delivery” (no error recovery, no reordering of data or retransmissions)
• No flow control (sender determines the amount of data transmitted)

Question 3

Why would you ever use UDP?

Answer 3

• Realtime communication (there’s no way to stop and resend the data, time doesn’t stop for your network)
• Connectionless protocols (DHCP / TFTP)

Question 4

Why use TCP?

Answer 4

• Connection-oriented protocols prefer a “return receipt” (HTTPS, SSH)
• The application doesn’t worry about out-of-order frames or missing data (TCP handles the communication overhead, the app has one job)

Question 5

What’s an IPv4 socket?

Answer 5

• Server IP address, protocol, server application port number
• Client IP address, protocol, client port number

Question 6

What are non-ephemeral ports?

Answer 6

• Permanent port numbers
• Ports 0 - 1,023
• Usually on a server or service

Question 7

What are ephemeral ports?

Answer 7

• Temporary port numbers
• Ports 1,024 - 65,535
• Determined in real-time by the client

Question 8

What are port numbers?

Answer 8

• TCP and UDP ports
• Can be any number between 0 - 65,535
• Most servers use non-ephemeral port numbers, but that’s not always the case
• Port numbers are for communication, not security
• Service port numbers need to be “well known”
• TCP port numbers aren’t the same as UDP port numbers