Okay, so I'm going to set this to real-time to end the simulation.
Let's run another simulation.
And what I'm going to do on the PC is open up a different application.
You can see the web server has displayed the website on that server.
I'll close this down now.
So that was just a built in web server running on that internal server.
What I'll do here is let's start.
Email, let's compose an e-mail.
And in this example, the only email address used is Peter@Cisco.com going to our server again you
can see that we're running multiple services on the server.
We've got HTTP, TFTP, FTP but here
We've got an e-mail server.
The only user account I've configured on the server is Peter.
You could create a different one if you wanted to.
So you could add another user for yourself.
We've got two e-mail services running here simple mail transfer protocol is MTP and POP 3, POP
3 is an older protocol that allows us to retrieve e-mail from an email server is MTP
allows us to transmit e-mail these protocols use different port numbers
So let's actually show that practically.
So test e-mail, test e-mail
showing port numbers before I click send.
I want to make sure that I'm running simulation mode which I am and now I'll click send SMTP uses
TCP looking at that TCP message, inbound PDU, we have our source and destination MAC addresses.
PC talking to the server PCIP address talking to the server IP address.
So layer 2, layer 3 this is IP version 4
Again just to recap make sure that you know this stuff at layer 2,the type field indicates that the
protocol at layer 3 is IP version 4, IP version 6 has a different protocol number.
We know the protocol at layer 4 because of this number TCP.
So that indicates TCP at layer 4, destination port number is 25, what is 25 looking at the IANA
Website port 25 is simple mail transfer it's empty.
So random port number, or ephemeral port number going to port 25.
So we are sending an email to the server using SMTP so push that along.
So we've got our TCP what's called the three way handshake that takes place so we have to use what are
called synchronization bits and it has to be an acknowledgement.
I'll talk about that in a separate video but notice here we've got our inbound PDU going to the server
once again source port number destination port number at layer 4(*layer 7)
You can see SMTP data
So we are sending data to the server this will be our actual email going to the server.
And now the server replies back looking at that.
The message to the PC, notice port 25 talking to the agreed port number of 1027 SMTP data.
Another reason we have the TCP handshake is we have to agree what port numbers we're going to be talking
on.
If you choose a random port number to talk to me how will I know what your random port number is.
You need to tell me that or your ephemeral port number you need to tell me what that is.
Notice also we have sequence numbers and acknowledgments in the messages so that takes place.
And now suddenly we've got some more TCP, let's have a look at that TCP message inbound PDU still
using port 25 so a bunch of TCP messages
I run out of space there
so my packet tracer has locked up so I'm going to restart it.
This may happen sometimes with packet tracer.
Now you may encounter problems like this in Packet Tracer.
Just bear with the application it's not perfect but it's well worth the trouble because you'll learn
a lot to using this application.
Cause I didn't get my email.
Let's try that again someone to send it to Peter@cisco.com, test to, test to send my email now
To retrieve my email,
I'm going to go to simulation mode and I'm going to click retrieve, to get my email from the server.
So what have we got here,
what message is this, notice
this is TCP but the port number is 1 1 0, what is 1 1 0 on the IANA website.
We can see that this is Post office Protocol Version 3 or POP 3.
So this is the protocol used to retrieve the message from the server.
So here's the actual POP 3 message.
Let's have a look at that inbound means it's inbound to the switch.
So it will be the same inbound and outbound on the switch.
Source MAC address is PC, destination MAC addresses is server, type is 800 telling us that it's IP version
4 source and destination IP address is PCI and server, protocol use at Layer 4 is TCP we can see that
here.
Source port number used by the PC is this, destination port number is 110.
This is POP 3 data so that will go to the server, message goes back to the PC we've got some TCP messages
I'll clear my event list, it's got a real-time and then hopefully on my PC what you can see is I've
received my messages now, see here's my original message.
Actually that's been retrieved from the server and here's my test to message that was received from
the server.
Now I can spend a long time showing you different protocols here as an example you could open up a command
prompt and then open up FTP to the server and log in as Cisco Cisco username Cisco password Cisco and
use the command DRR to see the files on the server if you ran simulation mode you'd be able to see
those messages to the server.
So spend some time having a look at the different protocols use email, use HTTP, use FTP to see the messages
and the protocols, simulation mode in packet tracer's
great to actually see what's going on.
So fantastic way to actually learn the protocols.