Original subtitles

So again protocol at Layer 4 is TTP which Layer 7 protocol is used.

Notice destination port is 80 80 is HDP.

Notice we've got what's called a destination port we could search in Google for port numbers and let's

go to the eye on a Web site which is the Internet Assigned Numbers Authority and if we search for 80

in that list you can see that HP port 80 is world wide web.

A GDP.

Now some protocols such as DNS or domain name server or domain name system as it's sometimes called

uses both DCP and UDP HDP generally uses TTP because we want reliability.

So again Layer 3 protocol is IP version 4 Layer 4 protocol is TTP we are indicating the application

that we want to send the data to by the port number.

Think of it as follows The server is running multiple services and I want you to see these services

and look at the protocols going to the services.

So under services we've got an HP server.

We've also got a TFT P server.

We've got an FTB server and email server and various other servers.

Where should the data go.

It needs to go to the right application.

You're not going to open up a MP 3 music file in a word processor.

It's not going to work.

Word opens word processing files an application such as a music application gets used to open music

files.

So you need the right application or right service to work with the right data.

So again you use a port number to send the ATP traffic to the HP server you use a port number like 53

to send traffic to a DNS server.

You use Port 21 to send it to FCP server or service sixty nine to a TFT IP service.

You have one physical server running different processes or different applications and you want to send

the data to the correct service or correct server application.

Those applications listen on a specific port number.

So the HDP server listens and port 80 the NDP server will listen on Port 21 TFT people listen on Port

69.

So this is indicating to the server that this data needs to go to the application listening on port

80 and you can see the HBP request.

So packet gets sent to the server the server because it's listening on that port will receive the data

and send it to the relevant application.

What you'll also notice here is the source port is 1025.

So let's talk about port numbers and a bit more detail.

A server service will listen on what's called a well known port number but when you initiate a session

to a well-known port number such as 80 you will use what's called a femoral or random port number.

Now going back to the Iona we told that service names are assigned on a first come first serve basis

as documented in this or if sea service names and port numbers are used to distinguish between services

that run over transport protocols such as TCB UDP and others.

This is the important part.

These port numbers in the range 0 to 1023 are signed as system port numbers so 80 is in that range.

We have what's called a user port numbers in this range and then we have what are called dynamic or

private port numbers also called ephemeral port numbers.

Again people use different terms.

Is it a router.

Is it a router.

Is it a highway or a motorway.

Is it a sneaker.

Is it a trainer or in South Africa.

Is it a tacky tacky as a word that comes from Afrikaans.

But we use that as the English word in South Africa.

So is it a tacky.

Is it a trainer.

Like in the UK.

Was it a sneaker in the USA.

Different terms used by different people but dynamic or random port numbers or private port numbers

or ephemeral port numbers are dynamically or randomly used.

Now you'll notice packet traces actually using a port number in this range 1025 is the source port number

things change over time if I do a search in Google for a femoral port numbers

on Wikipedia.

You can read more detail about how the eye honor recommends those port numbers for dynamic or private

ports.

But many Linux kernels use this range BSD used this range.

Windows XP used this range by default.

So 1025 not 1024 Vista.

Windows 7 2008.

You use the AI on a range Windows 2003 used this range basically different operating systems used different

ranges and then we told all versions of Windows since Windows 2000 to allow you to specify a custom

range in that range 1025 to sixty five thousand five hundred and thirty five.

You can also see that Windows allows you to customize this so you can specify a custom range.

The moral of the story is servers and for the CCMA you need to worry about some of the well-known port

numbers 80 HDP 21 f DP 69 TFT P and there's a few others.

23 is telnet.

22 is SS H.

No the well-known protocols HDP s as an example is 443 you'll get to know the protocols as you work

with networks.

But for the exam study the well-known port numbers and well-known protocols.

So here we can see the pieces using this source port number going to the server.

However what you'll notice and let's show that in the PD you is that the port numbers get swapped round

when the server replies.

So this is the inbound PD.

This is the PD you from the P.C. to the server.

Source mac addresses the P.C. source IP addresses the P.C. source port number is 1025.

But for the reply that gets reversed round source MAC address is the server.

Destination is the P.C. source IP addresses the server destination is the P.C. source port number is

80.

Destination Port number is 1025.

So basically for our communication MAC addresses get swapped round IP addresses get swapped round and

port numbers get swapped round.

So if you talk from your P.C. to my server and port 80 I'll reply from port 80 to the port number that

you've chosen.

The reason why the PRC will choose dynamic port numbers is if you open up two sessions to my server

your first session may use port number 1025 and your second session may use port number one thousand

twenty six.

They should be randomize but often they're not and that's why hackers can often guess what port number

is going to be used next by application but there you go.

That's an example of layer to layer 3 layer for and layer 7.

If we look in the OSA model here they don't show Layer 7 as the protocol here but that's actually the

protocol used in the TPP IP protocol stack.

Again TTP IP model originally 4 layers we now have 5 layers.

So we group layer 5 6 and 7 together as the application.

But we talk about Layer 7 because of the history with the OSA model.

Okay so that was quite detailed.

I'm hoping that helps you understand a bit about port numbers protocol numbers Ethernet types and so

forth.

In the next video I'm going to show you another protocol.

Let's use email and let's say FCP spend some time however going through this yourself having a look

at the different protocols.