CompTIA A+ 220-1201 (2.1 - Introduction to IP)

A series of moving vans

• Efficiently move large amounts of data

- Use a shipping truck

• The network topology is the road

- Ethernet, DSL, cable system

• The truck is the Internet Protocol (IP)

- We've designed the roads for this truck

• The boxes hold your data

- Boxes of TCP and UDP

• Inside the boxes are more things

- Application information

TCP and UDP

• 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

TCP - Transmission Control Protocol Communication

TCP - Transmission Control Protocol

• Connection-oriented

- A formal connection setup and close

• "Reliable" delivery

- Recovery from errors

- Manages out-of-order messages or retransmissions

• Flow control

- The receiver can manage how much data is sent

UDP - User Datagram Protocol Communication

UDP - 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

Why would you ever use UDP?

• 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)

• The data might not get through

- The application keeps track and decides what to do

- It might not do anything

Communication using TCP

• Connection-oriented protocols prefer a "return receipt"

- HTTPS (Hypertext Transfer Protocol Secure)

- SSH (Secure Shell)

• The application doesn't worry about

out of order frames or missing data

- TCP handles all of the communication overhead

- The application has one job

Speedy delivery

• 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

Lots of ports

• IPv4 sockets

- Server IP address, protocol, server application port #

- Client IP address, protocol, client port number

• Non-ephemeral ports - permanent port numbers

- Ports 0 through 1,023 - Usually on a server or service

• Ephemeral ports - temporary port numbers

- Ports 1,024 through 65,535

- Determined in real-time by the client

Port numbers

• 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