2.1 - Introduction to IP

Question 1

TCP and UDP

Answer 1

• Transported inside of IP
  – Encapsulated by the IP protocol
• Two ways to move data from place to place
  – Different features for different applications
• OSI Layer 4
  – The transport layer
• Multiplexing
  – Use many different applications at the same time
  – TCP and UDP

Question 2

TCP

Answer 2

• Transmission Control Protocol
• Connection-oriented
  – A formal connection 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 3

UDP

Answer 3

• 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 4

Why would you ever use UDP?

Answer 4

• Real-time communication
  – There’s no way to stop and resend the data
  – Time doesn’t stop for your network
• Connectionless protocols
  – DHCP (Dynamic Host Configuration Protocol)
  – TFTP (Trivial File Transfer Protocol)

Question 5

IP delivery process

Answer 5

• The IP delivery truck delivers from one (IP) address to
  another (IP) address
  – Every house has an address, every computer
  has an IP address
• Boxes arrive at the house / IP address
  – Where do the boxes go?
  – Each box has a room name
• Port is written on the outside of the box
  – Drop the box into the right room

Question 6

IPv4 sockets

Answer 6

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

Question 7

Non-ephemeral ports

Answer 7

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

Question 8

Ephemeral ports

Answer 8

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

Question 9

Port numbers

Answer 9

• TCP and UDP ports can be any number between
  0 and 65,535
• Most servers (services) use non-ephemeral
  (not-temporary) port numbers
  – This isn’t always the case
  – It’s just a number.
• 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