All language subtitles for Free-CCNA-TCP-UDP-Day-30-CCNA-200-301-Complete-Course_en

This is a free, complete course for the CCNA.

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In this video we will cover two very\n

These protocols are mentioned in exam topic\n

I could spend hours covering the details of\n

you just need a high-level understanding of\n

Here’s what we’ll cover in this video.

First up, the basics of Layer 4.

We’ve already covered a lot regarding Layers\n1, 2, and 3.

For example, at Layer 1 we covered the most\n

At Layer 2 we covered things like MAC addresses,\n

At Layer 3 we covered things like IP addresses\nand routing.

Now I think is a good time to talk about Layer\n4.

After a basic overview of Layer 4, I will\n

After that, I will introduce UDP, User Datagram\nProtocol.

UDP is much simpler than TCP, and it’s easiest\n

Remember, that is the exam topic, compare\nTCP to UDP.

As always, make sure to watch until the end\n

from Boson ExSim, the best practice exams\n

If you want to get Boson ExSim, follow the\n

So let’s cover some basic functions of Layer\n4 protocols.

First up, Layer 4 provides transparent transfer\n

To briefly explain what that means, here’s\n

when I covered the OSI Model and TCP/IP Suite.

This up here shows the network topology, with\n

It encapsulates the data with a Layer 4 header,\n

Layers 3, 2, and 1, to deliver the data unchanged\n

The hosts themselves aren’t aware of the\n

of data is ‘transparent’ to them.

Another function of Layer 4 protocols is to\n

You’ll soon see that TCP provides these\n

What are some of these services?

That means making sure that the destination\n

Another service is error recovery.

If an error occurs in transmission, Layer\n

Next is data sequencing, making sure that\n

of order, the end host can sequence it in\nthe correct order.

One more is flow control, making sure that\n

than the destination host can handle.

These are services provided by TCP but not\nUDP.

I’ll explain further later, so don’t worry\n

Okay, one more function of Layer 4 is to provide\n

These addresses are called ‘port numbers’.

Note that the word ‘port’ can also refer\n

to on network devices, but the Layer 4 port\n

These port numbers provide a few functions,\n

Layer protocol that is being used.

Another is to provide something called ‘session\nmultiplexing’.

Let me explain these concepts.

Here we have PC1, and it will access resources\n

Let’s see how these ports are used to identify\n

sessions between PC1 and the servers.

First of all, what is a session?

It’s simply an exchange of data between\n

And in your daily use of your PC, your PC\n

Perhaps you have multiple Internet tabs open,\n

You probably have multiple services running\n

In PC1’s case, let’s say it is communicating\nwith SRV1.

At Layer 4 it is using TCP, and it uses a\n

What are these ports used for?

The destination port is very important, it\n

For example, TCP port 80 is used for the protocol\n

So, perhaps SRV1 is hosting a webpage that\nPC1 wants to access.

Now, how about the source port?

It’s randomly selected by PC1, and in combination\n

For example, after SRV1 receives PC1’s message\n

In SRV1’s reply, notice that the source\n

the source port is 80 and the destination\nis 50000.

When PC1 receives this message, the source\n

it’s part of the same communication session\n

What if PC1 opens up a separate connection\nto SRV1?

It might be using HTTP at destination port\n

SRV1’s response will use that source port\n

so PC1 knows it’s part of that session.

But PC1 wants to access something on SRV2\nat the same time.

It uses a TCP destination port number of 21,\n

TCP port 21 is used for FTP, the File Transfer\nProtocol.

As the name suggests, it is used to transfer\nfiles.

SRV2’s reply will reverse the port numbers,\n

These will tell PC1 that this communication\n

Okay, I hope that gave you a basic understanding\n

protocol, such as HTTP, the Hypertext Transfer\n

or FTP, the File Transfer Protocol which is\n

I also showed how these numbers are used by\n

The port numbers that Application Layer protocols\n

They have designated the following ranges.

Well-known port numbers are ports 0 through\n1023.

These are used for major protocols like HTTP,\n

Registered port numbers are in the range 1024\nto 49151.

Registration is required to use these port\n

Finally, the range 49152 through 65535 is\n

Hosts use this range when selecting the random\nsource port.

Note that in the previous example, all of\n

came from the ephemeral port range.

Finally, note that port numbers are a function\n

Next I’ll explain each of the protocols,\n

earlier, reliable data transfer, error recovery,\n

I’ll give an overview of it’s functions,\n

and then I’ll go more in depth on a few\nof its functions.

First up, TCP is a connection-oriented protocol.

Well, before actually sending data to the\n

Once the connection is established, the data\nexchange begins.

The source host doesn’t just start sending\n

destination host and setting up this connection.

Next, TCP provides reliable communication.

The destination host must acknowledge that\n

Remember, segment is the name of the Layer\n

Then, if the source host doesn’t receive\n

In the next slide you’ll see that there\n

The sequence numbers in the TCP header allow\n

order even if they arrive out of order.

Okay, last thing for now, TCP provides flow\ncontrol.

That means that the destination host can tell\n

rate that data is sent, so that it isn’t\n

Okay, now let’s take a look at the TCP header,\n

As you can see, there are quite a few different\n

provide all of those different services I\n

The good news is, you don’t have to learn\n

I just want to briefly point out a few important\nfields.

First up, the source and destination port\nfields.

Note that each field is 16 bits, 2 bytes,\nin length.

That means there are a total of 65536, which\n

The next two fields are the sequence number\n

These two fields are used to provide sequencing\n

TCP has a series of ‘flag’ bits which\n

I want to mention these three, ACK, SYN, and\nFIN.

These three flags are used to establish and\n

In the next slide I’ll explain those processes\nmore.

The final field I want to point out is the\nWindow Size field.

This field is used for flow control, adjusting\n

Okay, that’s all for the TCP header.

You don’t have to learn every field or memorize\n

I mentioned that TCP is connection-oriented,\n

a connection before actually sending data.

The method TCP uses to establish connections\n

It has that name because it involves three\n

So, let’s say PC1 wants to access a webpage\non SRV1 using HTTP.

First, it must establish a TCP connection.

To do so, it uses these two flags in the TCP\n

acknowledgment, and SYN, meaning synchronization.

First, PC1 will send a TCP segment to SRV1\n

That is part one of the three-way handshake.

Next, SRV1 will reply by sending a TCP segment\n

That is part two of the three-way handshake.

Finally, PC1 will send a TCP segment with\nthe ACK bit set.

Now the three-way handshake is complete and\n

The real data exchange can then begin, the\n

handshake, are just to establish a connection.

Make sure to remember the three-way handshake.

Now let’s talk about how TCP terminates\nconnections.

This process, sometimes called the TCP ‘four-way\n

When PC1 decides that it no longer needs the\n

process to terminate the connection.

The process uses these two flags in the TCP\nheader, FIN and ACK.

First, PC1 sends a TCP segment to SRV1 with\nthe FIN flag set.

Finally, PC1 sends an ACK in response to SRV1’s\n

Here’s the same summary I showed you before.

So, can you see what ‘connection-oriented’\nmeans?

Before actually exchanging data, PC1 and SRV1\n

Okay, now let me demonstrate how TCP uses\n

the header to provide reliable communication\nand sequencing.

So, let’s look at an exchange between two\nPCs, PC1 and PC2.

When PC1 sends the three-way handshake’s\n

number, let’s say it sets it to 10.

Then, when PC2 sends the SYN-ACK to PC1, it\n

Not only that, it also acknowledges that it\n

of 10, by setting the acknowledgment field\nto 11.

That’s because TCP uses something called\n

Instead of acknowledging sequence number 10\n

sequence number of the next segment it expects\nto receive.

So continuing that process, PC1 sends the\n

The sequence number is 11, and using forward\n

PC2 replies with a sequence number of 51,\n

a value of 12 in the acknowledgment field.

Then the exchange continues, like this.

So, what should you remember from this?

Remember that hosts set a random initial sequence\n

used to indicate the sequence number of the\n

Okay, so now I’ve shown how the sequence\n

are used to acknowledge that the host has\n

These sequence numbers also allow hosts to\n

for some reason they arrive out of order.

If a segment isn’t acknowledged, it is sent\nagain.

To simplify things, I will only show one set\n

So, PC1 sends SRV1 a segment with sequence\nnumber 20.

Using forward acknowledgment, SRV1 sends Ack\n21 to PC1.

PC1 then sends Sequence number 21, but for\n

After waiting a certain amount of time with\n

This is called TCP retransmission.

This time SRV1 receives it, and sends Ack\n

Okay, that’s a very brief overview of how\n

Finally, let me introduce how TCP provides\nflow control.

Acknowledging every single segment, no matter\n

However, the TCP header’s window size field\n

A host could send three segments, with sequence\n

In addition, a ‘sliding window’ is used\n

The window size is increased as much as possible\n

size backs down to a more reasonable level,\n

Okay, before moving on let me point out one\nthing.

In all of these examples, I used very simple\nsequence numbers.

In real situations, the sequence numbers get\n

each message, especially when the sliding\n

For the CCNA, just understand the concepts\n

Okay, so that was a very brief overview of\n

It would take hours to cover all of the details,\n

The details I did show you about sequence\n

just to help you understand the basic concepts.

Remember, the exam topics state that you need\n

you need to understand the detailed mechanics\n

Now that you’ve seen some of what TCP provides\n

UDP is much simpler, so I’ll sum it up in\none slide.

UDP is not connection-oriented.

Unlike TCP, in UDP the sending host does not\n

UDP does not provide reliable communication.

When UDP is used, acknowledgments are not\n

If a segment is lost, UDP has no mechanism\nto re-transmit it.

Segments are sent ‘best-effort’.

You might not be familiar with the term best-effort.

Basically, it means UDP provides no guarantee\n

It sends it, it makes the effort, but it doesn’t\n

UDP does not provide sequencing.

Unlike TCP, UDP has no sequence field in its\nheader.

If segments arrive out of order, UDP has no\n

Finally, UDP does not provide flow control.

It has no mechanism like TCP’s window size\n

Let’s take a look at the UDP header.

, thanks again to Wikipedia for the image.

Source and destination port numbers, a length\n

and a checksum so the receiving host can check\nfor errors.

In the next slide let’s compare TCP and\nUDP.

First up, here are the two headers for comparison.

All of the additional fields that TCP has\n

like sequencing and error recovery.

So, in which cases would TCP be used, and\n

TCP provides more features than UDP, but at\n

In addition, acknowledgments and retransmissions\n

For applications that require reliable communications,\n

You wouldn’t want to download a PDF file\nwith a page missing.

You want to make sure you get the whole file.

On the other hand, for applications like real-time\n

phone calls, Zoom, Skype, etc, UDP is preferred.

These applications are very delay-sensitive,\n

One thing to note is that there are some applications\n

such within the application itself.

TFTP, the Trivial File Transfer Protocol,\nis such an example.

I’ll cover it later in the course.

Also, think about a Skype call.

If you’re talking to someone over Skype\n

you can simply ask the other person to repeat\nwhat they said.

In effect, you are asking for a ‘retransmission’.

Finally, there are some applications that\n

DNS, the Domain Name System, is an example.

Here’s a chart summarizing the differences\nbetween TCP and UDP.

But don’t forget, both TCP and UDP provide\n

These port numbers identify Application Layer\n

They are both Layer 4 protocols, so they both\n

Finally, I will list some important well-known\n

We haven’t really covered any of these Application\n

taking the time to memorize the port numbers\nnow.

I will provide flashcards in the flashcard\n

I will, however, mention the port numbers\n

the course, so if you prefer you can learn\n

First up, FTP, the File Transfer Protocol,\n

SSH, Secure Shell, which is commonly used\n

Telnet, which can also be used to connect\n

SMTP, the Simple Mail Transfer Protocol, is\n

HTTP, Hypertext Transfer Protocol, commonly\n

POP3, Post Office Protocol 3, used for retrieving\n

And finally HTTPS, Hypertext Transfer Protocol\n

Okay, let’s list some protocols that use\nUDP.

DHCP, Dynamic Host Configuration Protocol,\n

IP address and other things, uses UDP ports\n67 and 68.

TFTP, the Trivial File Transfer Protocol,\nuses UDP port 69.

SNMP, the Simple Network Management Protocol,\n

Finally, the only protocol you should be aware\n

It usually uses UDP, but uses TCP in some\nsituations.

Okay, to help you review I have added a ‘portnumbers’\n

Here’s how you can use it to review these\nspecific cards.

Select ‘study by card state or tag’.

Then select ‘all cards in random order (don’t\nreschedule)’.

Finally click on ‘choose tags’.

Check ‘require one or more of these tags’\n

Also make sure it isn’t highlighted under\n

Now you will be able to review the cards without\n

After you have reviewed them, you can simply\n

Do it until you answer them all perfectly.

By the way, if you have questions about Anki\n

are having trouble getting the custom study\n

I’m no Anki expert and it’s hard for me\n

Before moving on to the quiz, let’s review\nwhat we covered.

We covered the basics of Layer 4, including\n

We took a look at TCP, a Layer 4 protocol\n

such as reliable communication and flow control.

Then we looked at UDP, which doesn’t provide\n

a smaller header with less overhead.

Finally, we spent some time comparing the\ntwo protocols.

Remember the exam topics list, you’re expected\n

Watch until the end of the quiz for a bonus\n

Okay, let’s go to quiz question 1.

Which of the following is a well-known port\n

Pause the video to think about your answer.

Here are the ranges designated by IANA.

Well-known port numbers are those from 0 through\n1023.

Answers B and C are in the Registered range,\n

Okay, let’s move on to question 2.

According to IANA specifications, what range\n

randomly selecting a source Layer 4 port number?

Pause the video to think about your answer.

The destination port number depends on the\n

port number should be randomly selected from\n

Once again, here are the different port ranges\n

Note that D, reserved, isn’t one of the\nranges.

Which of the following are features of TCP\nbut not UDP?

Pause the video to think about your answers,\nselect three.

The answers are B, error recovery, D, flow\n

Layer 4 addressing in the form of port numbers\n

TCP and UDP, but only TCP provides services\n

Which of the following Application Layer protocols\n

Pause the video to think about your answers,\nselect three.

The answers are A, SMTP, C, HTTPS, and F,\nSSH.

Although we haven’t learned the details\n

which ones use TCP or UDP, and their port\nnumbers.

You’ll definitely need to know some of them\nfor the test.

Okay, let’s move on to question 5.

PC1 and SRV1 have an active TCP connection.

SRV1 receives a TCP segment from PC1 with\n

When SRV1 acknowledges the segment, what will\n

Assume a TCP window size of 1.

Pause the video to think about your answer.

The answer is C. TCP uses ‘forward acknowledgment’,\n

segment by stating the next segment it expects\nto receive.

If SRV1 acknowledged with a value of 27, for\n

receive the segment with sequence number 27,\n

Don’t worry too much about the details of\n

understanding of how sequencing and acknowledgment\nworks.

Okay, that’s all for the quiz.

Let’s take a look at a bonus question in\nBoson ExSim for CCNA.

Here's today's Boson ExSim practice question.

So, I will click on Launch Simulator and here\n

Select the applications layer protocols on\n

All application layer protocols will be used.

So, these here on the left are all application\n

layer protocols we just learned, TCP and UDP.

And also one of these uses both TCP and UDP.

Okay, so pause the video here and think about\nthe answer.

So I will go from top to bottom.

DNS, Domain Name System, that uses TCP and\nUDP.

Usually it uses UDP, but it does use TCP in\nsome cases.

FTP, File Transfer Protocol, TCP.

SMTP, Simple Mail Transfer Protocol, TCP.

And then these last two, of course UDP.

SNMP, Simple Network Management Protocol.

And TFTP, the Trivial File Transfer Protocol.

Okay, so I will click on 'done'.

So, if you want to read Boson's explanation\n

I haven't explained all of these application\n

For now just remember whether they use TCP\n

Okay, so that's Boson ExSim for CCNA.

I highly recommend these practice exams.

I used them when I was studying for my CCNA\n

because they really helped me pass my exams.

So, if you want to get a copy of Boson ExSim,\n

There are supplementary materials for this\nvideo.

There is a flashcard deck to use with the\nsoftware ‘Anki’.

This time there won’t be a packet tracer\n

demo, to show you TCP and UDP in action in\na real network.

Wireshark is a packet capture program, which\n

It’s great for studying and also a very\n

Before finishing today’s video I want to\n

To join, please click the ‘Join’ button\nunder the video.

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