TCP and UDP - CompTIA A+ 220-1101 – 5.10

Video Description

Let’s have a look at TCP and UDP. Download PowerPoint: https://itfreetraining.com/handouts/ap11/5c05.pptx TCP and UDP TCP stands for Transmission Control Protocol. The protocol guarantees a connection and delivery of packets over the connection. You will often hear this protocol referred to as connection-oriented. For the exam, know that TCP is connection-oriented and that means guaranteed connection and delivery. You may get a question on it. The other method of transmitting data is UDP, or User Datagram Protocol. This protocol is "fire and forget." Thus, it is often referred to as connectionless. Make sure you know the difference between the two. I will take a deep dive into the protocols to help you better understand how they work. For the A+ exam, you only need an understanding of the basic concepts. When I have finished the deep dive, I will give you a summary of the major points. Let's have a closer look at these protocols. TCP 3-Way Handshake TCP uses a 3-Way handshake, which essentially is a three-step process used to create a connection. To understand how it works, consider that you have a client computer. The client computer wants to make a connection to a server. In order to do this, the client sends a SYN message to the server, SYN being short for synchronize. The SYN message configures certain values, for example, a random sequence number. More on that later in the video. The server sends a SYN-ACK message back. This message acknowledges that the SYN message was received and the server sends its own SYN which will be a random sequence number. More on that later in the video, I promise. The last message is an ACK message. This message is from the client to tell the server that the configuration and sequence numbers have been agreed upon. Essentially, a TCP 3-way handshake has been done so both sides can negotiate parameters before data transmission. Once the final acknowledgment is sent, both sides are now ready to send data. Now that we understand what the 3-way handshake is, let’s have a look at the sequence number. Sequence Number A sequence number is a number representing the number of bytes sent in the data stream. The data is sent in segments, which can vary in size. The sequence number is used to acknowledge to the sender how much data the receiver has received. The first sequence number is randomized, and I will go into more detail shortly about why this occurs. To make things easy to understand, it is often better to work with a relative sequence number. The relative sequence number is a count of the actual bytes subtracted from the random start sequence number. I will go into more detail shortly, so don’t worry if this sounds confusing at first. The reason that sequence numbers are used is that they allow for the number of bytes received to be acknowledged. This is how TCP achieves reliable communication. Each data segment, when received, needs to have an acknowledgment message sent back. Updates in the TCP protocol allow multiple segments to be acknowledged at once. More on that later in the video. If a segment is lost during transmission, having a sequence number allows for the missing data segment to be retransmitted. Now that we understand sequence numbers, the next question is why is it initially randomized? Random Initial Sequence Number The initial sequence number is random to help prevent impersonation and denial of service attacks. If an attacker is not able to predict what the sequence number is, it makes it harder for them to affect the traffic traveling over that data stream. To understand how making a connection works, consider that you have a client attempting to make a connection with a server. The client will send the SYN message to the server. The SYN message will contain a random sequence number. Description too long for YouTube. Please see the following link for the rest of the description. https://itfreetraining.com/ap11/5c05 References “The Official CompTIA A+ Core Study Guide (Exam 220-1101)” pages 184 to 186 “Mike Myers All in One A+ Certification Exam Guide 220-1101 & 220-1102” pages 783 to 784 Credits Trainer: Austin Mason http://ITFreeTraining.com Voice Talent: HP Lewis http://hplewis.com Quality Assurance: Brett Batson http://www.pbb-proofreading.uk