Time
23 hours 21 minutes
Difficulty
Intermediate
CEU/CPE
14

Video Transcription

00:02
I welcome back to the course in the last video, we went over a brief introduction on scan E.
00:07
In this video, we're gonna talk about the TCP or transmission control protocol three way handshake.
00:12
So on the screen, you see, I have host a had host be
00:16
so we're gonna pretend that I'm host a and that your host be
00:20
so I want to talk to you. I see you across the room and I want to go have a conversation with you.
00:25
So I send you a sin packet, which stands for synchronization.
00:32
And I'm basically saying in here that hey, I want to talk.
00:35
And so with my sin packet, I'm gonna have a sequence number. So in this case will say it's 100.
00:42
You decide that you do want to talk to me, so you send me back an acknowledgement.
00:48
So a C K packet
00:51
and what you're gonna do is you're gonna increment my
00:54
packet, my sequence number by one. So in this example, you're going to do 101 and you're basically responding. Say yes. I do want to talk.
01:02
You're also gonna send me back your own sin packet
01:07
and Essentially, you're just asking me, You know, Do you want to talk to me?
01:10
And we're just Just say your sequence number on that is 300.
01:14
So I send you a sin packing, and I say, Hey, I want to talk
01:18
and I've got my secrets number of 100.
01:19
You decide. You do want to talk to me. You send me an acknowledgment packet back with the secrets number and increment mind by one. So you increase it by one.
01:29
And then you also send me your own sin packet saying I do want to talk to you. Do you want to talk to me?
01:36
And of course I do, Right. I I'm the one who reached out to you first. So I send you back an acknowledgment packet,
01:42
and I'm gonna increase or increment your
01:47
sequence number. So you're 300. I'm gonna increase that by one.
01:53
So again, I want to talk to you. So I send you a packet
01:56
with my sequence number, and it says, basically Hey, I want to talk to you.
02:00
You send me a response back, you send me that acknowledgement saying, you know, I do want to talk to you And then you also send me your sin packet of saying, Do you want to talk to me
02:09
and again since I initiated this and of course I want to talk to you. I send you back an acknowledgement and I increments yours by one.
02:17
And I say yes, of course I want to talk to you in our communication is established.
02:23
So if you think of this in the context of
02:27
dating, you know, or or asking somebody to a dance. So I go up to the person I like and I say, Hey, I want to talk to you about something so I send my sin packet.
02:37
They decide they want to talk to me about whatever it is. So they acknowledge me the increment, this buy one.
02:43
They also send me their sin packet and say, Hey, do you want to talk to me as well?
02:46
And of course I do. Right. I walked up to them talk about the dance, so
02:51
I send them in knowledge from back saying, Yes, I do want to talk to you and then we communicate. We establish our communication stream. We start talking about the dance on Friday night
03:00
and Eventually I asked the person to the dance.
03:04
So in this video, we talked about TCP three way handshake.
03:07
So
03:08
again, how do we start this communication? Think about that for a minute. What do we need to send first? If we're trying to talk to the other person,
03:20
Correct? Yes. Yes. If you guessed a sin packet first you are correct.
03:24
And then how does the other person acknowledge that they got our message And they and then also basically ask us Hey, do you really want to talk to me?
03:35
Correct. Yeah. They send us in acknowledgement. Now they anchor Men are secrets number by one.
03:39
They also send us their own sin. Pack it with their own secrets number. They're basically here saying Yes, I do want to talk. Do you want to talk to me?
03:46
And then since we started the communication, of course we want to talk to them. Right? So we send them back that acknowledgement packet and we increment their sequence number by one.
03:57
We're basically saying Yes, of course. I want to talk to you.
04:01
So again, in this video, we talked about the TCP three way handshake and the next video. We're gonna jump into a little more discussion on scanning

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Ken Underhill
Master Instructor at Cybrary
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