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OK so in packet trace going to start simulation mode on my windows P.C. I'm gonna connect via HDP to
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the server on the left which is 10 1 1 100.
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Notice nothing happens but when we go back here we can see that some packets have been created.
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First one is OP now on ethernet devices communicate using what's called a MAC address and MAC addresses
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are burnt in address on a network interface code.
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So I'm connecting from this P.C. to the server.
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The P.C. doesn't know the MAC address of the server.
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This is the MAC address of the P.C. and we can see that by going to the config of the P.C. go to foster
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Ethernet.
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Notice MAC address ends in eleven ninety nine.
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So this piece he is basically opting or requesting OP is a resolution protocol requesting the MAC address
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of the server.
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So it's basically saying who has this IP address so that gets sent to the switch.
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Now this is what's called a broadcast frame.
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Notice the destination is Fs.
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That's a broadcast basically saying who has this IP address.
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If we look at the PD you or protocol data unit what you'll notice is the target MAC addresses blank
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target IP addresses this.
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Now this is a broadcast and a layered to switch will flood the broadcast which basically says it sends
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it out of all ports so it gets sent to the server the server drops the message because it doesn't have
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the IP address requested by the P.C..
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This writer will also drop the packet but this server will reply back.
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So the inbound PD view is from the P.C. to a broadcast address but the reply is now from the server
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ending in 0 0 8 6 as its MAC address to the P.C..
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Notice how Packet Tracer uses 7 layers here.
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At the moment it only shows Layer 1 and 2 here.
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If we look at the inbound PDA you however at least 2 we have Ethernet at least three we have OP and
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in the outbound PDA view that's what we see something similar.
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Layer 2 Layer 3 OP target IP address is the P.C. source IP address is the server source MAC address
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is the server and we can see that by looking at the interface nodes 0 0 86 is the MAC address.
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So what happens now is that gets sent back to the switch and gets sent to the P.C..
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So now the P.C. knows the MAC address of the server and can communicate directly to the server.
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NOTICE THIS IS A T C P packet so in TTP before communication takes place they do what's called a three
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way handshake.
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They agree on certain parameters such as sequence numbers and how much data they can send and then an
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HDP packet is sent into the network.
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So if we look at the actual HDP and that's the one I want to concentrate on here.
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Let's look at the HDP packet or HDP message Packet Tracer shows this very nicely gigabit one zero form
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the switch receives the frame.
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So this interface receives the frame from the P.C. we've got Layer 1 and layer 2 information here.
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It's gonna be forwarded out of gigabit 1 0 2 so forwarded to the server.
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But let's look at the inbound PD you and outbound Peter you will protocol data unit in a lot of detail.
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Source MAC address is the P.C. destination MAC address is the server.
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We have a type field.
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How does one layer referred to the layer above it at layer to on Ethan.
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It uses a type field this type 0 800 in hexadecimal 0 extra means hexadecimal indicates that the higher
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layer protocol is IP version 4.
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We could have other protocols here like IP version 6.
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So if I go back to a OK packet and have a look at that.
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Notice the type field is different here.
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It's 0 8 0 6.
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That indicates OP.
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So when a device receives a frame at least 2 it needs to know which protocol to use.
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In other words which protocol stack to use.
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We can see that in Windows by going to control panel.
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And if we have a look at our adapter so this is the wireless adapter that I'm currently using and go
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to properties.
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What you'll notice is we have IP version 4 and IP version 6 2 protocols at layer 3 have been enabled
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on this P.C. when the P.C. receives frames of the wire.
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So when that P.C. receives data how does it know which protocol stack to use.
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In other words is it an IP version 4 packet or is it an IP version 6 packet.
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It's based on the type field at layer too.
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So the serve on the left here when it receives this HDP packet will know that it needs to use the IP
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version 4 protocol stack.
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If you send IP version 4 packets to IP version 6 it's not going to understand it in the same way that
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I have an English protocol stack and I have an off records protocol stack a much better English than
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I am and offer cons if I speak to you and say hey we're mortar on it.
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If you don't understand Afrikaans you're not going to understand what I'm talking about.
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If I say good morning how are you and use the English protocol stack that's gonna make a lot of sense
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if you speak multiple languages and you hear different languages your mind will just switch to that
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language very easily.
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But on a P.C. it needs to know which protocol stack or which language to use.
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So in this example IP version 4 is the layer 3 protocol.
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And here we can see IP version full source and destination ip addresses now.
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Same thing again.
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How does it know which protocol is being used at layer 4 Ethernet is the layer to encapsulation IP version
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for the layer 3 protocol TTP is the layer for protocol.
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This number here indicates so it's a 6 in hexadecimal or 6 in decimal indicates that the protocol used
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at layer 4 is TTP.
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You can find personal information easily by just searching for IP version 4 protocol numbers and then
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the eye honor website gives you a list of protocol numbers.
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So as an example TTP is protocol number 6 17 if we scroll down is a UDP TTP or transmission control
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protocol is reliable.
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Use a data gram protocol or UDP is not reliable.
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