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