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So again protocol at Layer 4 is TTP which Layer 7 protocol is used.
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Notice destination port is 80 80 is HDP.
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Notice we've got what's called a destination port we could search in Google for port numbers and let's
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go to the eye on a Web site which is the Internet Assigned Numbers Authority and if we search for 80
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in that list you can see that HP port 80 is world wide web.
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A GDP.
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Now some protocols such as DNS or domain name server or domain name system as it's sometimes called
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uses both DCP and UDP HDP generally uses TTP because we want reliability.
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So again Layer 3 protocol is IP version 4 Layer 4 protocol is TTP we are indicating the application
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that we want to send the data to by the port number.
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Think of it as follows The server is running multiple services and I want you to see these services
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and look at the protocols going to the services.
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So under services we've got an HP server.
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We've also got a TFT P server.
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We've got an FTB server and email server and various other servers.
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Where should the data go.
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It needs to go to the right application.
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You're not going to open up a MP 3 music file in a word processor.
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It's not going to work.
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Word opens word processing files an application such as a music application gets used to open music
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files.
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So you need the right application or right service to work with the right data.
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So again you use a port number to send the ATP traffic to the HP server you use a port number like 53
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to send traffic to a DNS server.
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You use Port 21 to send it to FCP server or service sixty nine to a TFT IP service.
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You have one physical server running different processes or different applications and you want to send
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the data to the correct service or correct server application.
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Those applications listen on a specific port number.
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So the HDP server listens and port 80 the NDP server will listen on Port 21 TFT people listen on Port
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69.
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So this is indicating to the server that this data needs to go to the application listening on port
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80 and you can see the HBP request.
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So packet gets sent to the server the server because it's listening on that port will receive the data
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and send it to the relevant application.
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What you'll also notice here is the source port is 1025.
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So let's talk about port numbers and a bit more detail.
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A server service will listen on what's called a well known port number but when you initiate a session
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to a well-known port number such as 80 you will use what's called a femoral or random port number.
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Now going back to the Iona we told that service names are assigned on a first come first serve basis
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as documented in this or if sea service names and port numbers are used to distinguish between services
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that run over transport protocols such as TCB UDP and others.
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This is the important part.
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These port numbers in the range 0 to 1023 are signed as system port numbers so 80 is in that range.
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We have what's called a user port numbers in this range and then we have what are called dynamic or
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private port numbers also called ephemeral port numbers.
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Again people use different terms.
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Is it a router.
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Is it a router.
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Is it a highway or a motorway.
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Is it a sneaker.
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Is it a trainer or in South Africa.
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Is it a tacky tacky as a word that comes from Afrikaans.
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But we use that as the English word in South Africa.
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So is it a tacky.
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Is it a trainer.
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Like in the UK.
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Was it a sneaker in the USA.
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Different terms used by different people but dynamic or random port numbers or private port numbers
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or ephemeral port numbers are dynamically or randomly used.
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Now you'll notice packet traces actually using a port number in this range 1025 is the source port number
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things change over time if I do a search in Google for a femoral port numbers
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on Wikipedia.
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You can read more detail about how the eye honor recommends those port numbers for dynamic or private
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ports.
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But many Linux kernels use this range BSD used this range.
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Windows XP used this range by default.
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So 1025 not 1024 Vista.
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Windows 7 2008.
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You use the AI on a range Windows 2003 used this range basically different operating systems used different
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ranges and then we told all versions of Windows since Windows 2000 to allow you to specify a custom
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range in that range 1025 to sixty five thousand five hundred and thirty five.
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You can also see that Windows allows you to customize this so you can specify a custom range.
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The moral of the story is servers and for the CCMA you need to worry about some of the well-known port
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numbers 80 HDP 21 f DP 69 TFT P and there's a few others.
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23 is telnet.
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22 is SS H.
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No the well-known protocols HDP s as an example is 443 you'll get to know the protocols as you work
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with networks.
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But for the exam study the well-known port numbers and well-known protocols.
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So here we can see the pieces using this source port number going to the server.
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However what you'll notice and let's show that in the PD you is that the port numbers get swapped round
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when the server replies.
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So this is the inbound PD.
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This is the PD you from the P.C. to the server.
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Source mac addresses the P.C. source IP addresses the P.C. source port number is 1025.
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But for the reply that gets reversed round source MAC address is the server.
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Destination is the P.C. source IP addresses the server destination is the P.C. source port number is
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80.
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Destination Port number is 1025.
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So basically for our communication MAC addresses get swapped round IP addresses get swapped round and
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port numbers get swapped round.
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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
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you've chosen.
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The reason why the PRC will choose dynamic port numbers is if you open up two sessions to my server
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your first session may use port number 1025 and your second session may use port number one thousand
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twenty six.
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They should be randomize but often they're not and that's why hackers can often guess what port number
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is going to be used next by application but there you go.
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That's an example of layer to layer 3 layer for and layer 7.
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If we look in the OSA model here they don't show Layer 7 as the protocol here but that's actually the
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protocol used in the TPP IP protocol stack.
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Again TTP IP model originally 4 layers we now have 5 layers.
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So we group layer 5 6 and 7 together as the application.
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But we talk about Layer 7 because of the history with the OSA model.
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Okay so that was quite detailed.
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I'm hoping that helps you understand a bit about port numbers protocol numbers Ethernet types and so
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forth.
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In the next video I'm going to show you another protocol.
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Let's use email and let's say FCP spend some time however going through this yourself having a look
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at the different protocols.
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