WEBVTT

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 In this video I want to talk a little
 bit about web browsing and what

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 happens underneath the hood
 of your web browser.

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 Now this is not going to be a detailed
 look at all the ways that HTTP

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 works or that Java and Flash
 work and all of that.

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 Once again this is geared for the typical
 learner who knows how to open

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 up their browser but has no clue as to
 what's happening in the background.

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 And when they open up their browser
 and they try to go to website and

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 the website is not downloading at all
 or maybe part of its downloading

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 but an image in the website is not
 making it they have no idea why.

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 And so this will help sort of demystify
 that process a little bit.

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 So let's start with the basic question
 of what is a website right when

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 I go to INE.com or CNN
.com or something.

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 What makes up that website?

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 We can see here and you
 can just read this.

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 It is a collection of
 individual components.

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 So website is a whole bunch
 of things put together.

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 Text images such as JPEGs and GIFs,
 sounds, colors, links and formatting

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 that when providing the correct order
 creates a complete user experience.

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 How do you like that
 for a definition?

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 So the website has a name clearly and
 that name has to be resolvable to

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 an IP address. So there's going to
 be some server that is hosting this

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 website. So when we say that a server
 is a web server that's hosting a

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 website what we basically mean is that
 that server if a request comes

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 in saying hey I need INE.com.

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 That that web server either has all
 of the components of INE.com and has

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 all the images that
 go to that site.

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 It helps all the text that goes to that
 site or it knows where those things

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 are. It can go out and fetch them and
 then give them to the user that's

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 requesting them.

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 So all web starts start out as HTML
 which is a language indicating all

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 of the elements or files of the site
 and how they should be displayed.

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 So HTML is a formatting language.

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 And I'll show you here in just an example
 of what HTML looks like in case

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 you've never seen it before.

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 For those who've never seen it looks
 kind of cryptic and it's kind of

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 hard to figure out.

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 But basically what HTML is is when you
 see a document written HTML it's

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 saying look the text goes right here
 and HTML says this part of the text

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 should be bolded or this part
 should be italicized.

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 And here's where an image goes and
 here's the name of the image.

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 Here's the location of where
 that image can be found.

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 So HTML is sort of formatting saying
 where the components of the website

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 would fit and how it
 should be displayed.

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 So like I said a website is stored on
 a server that either contains those

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 assets locally in its own memory or
 knows where those assets are stored.

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 You might have one server that just
 has all of your graphics files on

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 it like your pictures
 and your movies.

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 You might have another server that has
 all the audio files on it, another

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 server that has all
 the text on it.

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 But the website would be stored on
 there would be some web server that

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 would say okay I know where all those
 things are and I can collect them

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 all and then give them to the
 user that's requesting them.

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 Now clearly there are other languages
 in addition to HTML that can be

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 used to build a website such as Java
 and Flash and PHP and all sorts of

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 other stuff. But for the basic CCNA
 entry level person we're just going

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 to focus on HTML as being the basic
 language to create a website.

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 So when dealing with web browsing there's
 really sort of two main protocols

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 that we need to be aware of.

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 HTTP and HTML. So in the event that you've
 never seen these acronyms before

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 let me define them for you.

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 HTTP stands for the hypertext
 transfer protocol.

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 Hypertext transfer protocol.

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 What is hypertext?

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 It's kind of interesting I've read several
 things that say hypertext is

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 text about text which
 is kind of weird.

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 It's basically if you hypertext is a
 language that says this is what the

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 font should look like.

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 This is how big something
 should be.

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 This is where on the web page this
 image should be displayed.

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 It should be four inches
 in and three inches up.

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 Hypertext is the language that sort
 of gathers all that stuff and knows

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 how to format the website into something
 that is pleasing for you to look

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 at. So HTTP is the protocol used to
 transfer hypertext from the website

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 to you, from the web server to your laptop,
 to your tablet, to your smartphone.

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 HTTP is the protocol that's being carried
 by IP, by the internet protocol.

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 And HTTP uses TCP.

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 I actually didn't have that in here
 but that is very important to know

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 that HTTP uses TCP at layer four and
 it has a well-known port number of

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 80. There is also HTTPS
 which is secure HTTP.

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 It's basically an encrypted
 form of HTTP.

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 Many websites these days are moving
 from HTTP to HTTPS because it's more

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 secure and if someone was able to sniff
 your packets and trans it, they

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 wouldn't really be able to decode them
 because everything has been encrypted

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 and only your laptop
 can decrypt it.

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 And HTTPS uses a different
 port number.

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 It's port number 443.

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 This is also carried in TCP.

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 And HTML is the hypertext
 markup language.

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 So this is actually the language that
 you use that you type in in your

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 text editor to sort of format a web
 page and to create a web page.

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 Here's an example.

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 If you've never seen HTML before, here's
 sort of a generic example of

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 what HTML looks like.

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 So different components of this, for
 example, head is indicating that

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 what's to follow between this
 section and this section here.

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 So all this stuff here is in a certain
 section of the document.

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 It's up towards the header, towards the
 top or the beginning of the document.

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 And then title is
 another HTML tag.

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 These things are all called
 tags, body, H1, nav.

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 These are all called HTML tags.

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 And a different tag indicates
 a certain thing.

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 A tag might indicate where on the web
 page this thing should be displayed

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 at the top, at the bottom, in the
 middle, on the left, on the right.

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 Or a tag might indicate that what's
 to follow is going to be an image

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 or it's going to be a line of text
 or it's going to be an audio file.

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 Or a tag might indicate formatting
 such as bold what I'm about to type

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 or apply a certain color to
 what I'm about to type.

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 So HTML is the process of applying all
 of these tags, creating a document

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 of tags that format the site so it looks
 the way you want to look like.

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 Because you and your head, you know,
 well, I want a picture to show up

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 in this section here and
 I want to be so big.

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 And I want text to show up down here
 and I want to be this certain color

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 and this certain font.

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 But you need to use these HTML tags
 to take what's in your head and make

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 it reality into a website.

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 So that's what HTML is.

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 And then HTTP takes all of this stuff,
 wraps it into an IP header and

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 transports it from the web server over
 to the browser in your laptop or

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 tablet. So how does HTTP work?

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 Well, number one, you know, within
 your browser, you type a URL like I

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&E.com or CNN.com.

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 It actually used to be that you would
 have to proceed your URL, which

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 is a uniform universal resource
 locator with www.

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 So those of you who have been working
 with the internet for any specific

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 period of time are probably used to
 typing in www.iony.com or www.google

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.com. But most browsers these days, if
 you don't type in www, which stands

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 for World Wide Web,
 just assume it.

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 So that's why most of these days you
 can just go to your browser and in

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 the URL bar, just type in INE.com or
 CNN.com and leave off the www because

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 it's so common it's just assumed.

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 And then DNS is involved.

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 So DNS is invoked as we saw in the
 previous video to resolve whatever

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 that name is that you typed
 in into an IP address.

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 From that point on, your laptop now
 invokes the TCP three-way handshake

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 on port 80 or port 443 to contact that
 destination web server that you've

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 just received the IP you
 addressed for via DNS.

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 After successful completion of the
 three-way handshake, now your local

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 browser will send its first HTTP message
 which is an HTTP get message.

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 And the get message you can see here,
 it'll specify things like a particular

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 directory where the web server website
 lives, the version of HTTP that

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 your client would prefer, some headers
 saying okay I would prefer the

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 website in English, I can support audio
 and video protocols, so headers

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 specifying the language and encoding
 that the client browser can prefer.

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 So just to give you an example of this,
 what I'm going to do is I'm going

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 to shut down my browsers
 here for just a moment.

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 So for those of you on the live stream
 I will not be able to see your

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 questions here for a moment.

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 Alright so I'm just going
 to bring this over here.

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 I'm going to start up a sniffer
 trace using wire shark.

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 And you know if you guys have never
 used wire shark, I would definitely

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 recommend you play around with it, it's
 free, you don't have to pay for

0:10:41.860000 --> 0:10:48.440000
 it, just go to wire shark.org
 and then you can download it.

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 And then I'm going to select my Wi-Fi
 adapter because that's the one I'm

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 using that's got most of my stuff right
 here, so here it is, wireless

0:10:54.460000 --> 0:10:56.400000
 network connection.

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 I'm going to create just some
 basic filters right now.

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 Let's see here, because I'm on the
 Wi-Fi there's all sorts of other IP

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 addresses here. So I don't want to
 see everybody at work, so I am 1071

0:11:12.780000 --> 0:11:26.580000
.96. So I just want to see this, I'll
 say IP.address equals 10.7.1.96.

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 So that will only show stuff coming
 to or going from my laptop.

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 So let's implement that.

0:11:35.580000 --> 0:11:40.400000
 Alright great. And then in addition to
 that, okay that looks pretty good.

0:11:40.400000 --> 0:11:51.560000
 So now what I'm going to do is I'm going
 to type in a URL of some website.

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 Let's see here, what's a
 website that we can use?

0:11:57.400000 --> 0:12:02.760000
 Let's go to something I
 haven't tried before.

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 The challenge here is that I want to
 show you HTTP and I want to show

0:12:07.380000 --> 0:12:11.160000
 you the types of messages are exchanged
 from my laptop when it's requesting

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 something and the information
 I get back.

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 The problem is a lot of websites
 these days revert to HTTPS.

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 And so even if you try to go to them via
 HTTP, all by itself it will revert

0:12:23.240000 --> 0:12:28.720000
 to HTTPS and why that is not good for
 this demonstration is that HTTPS,

0:12:28.720000 --> 0:12:29.920000
 everything is encrypted.

0:12:29.920000 --> 0:12:33.440000
 So you can't see any of those HTTP
 messages because they're encrypted.

0:12:33.440000 --> 0:12:37.380000
 So I'm just going to try to go to one
 or two websites that I hope are

0:12:37.380000 --> 0:12:41.180000
 using normal HTTP and not HTTPS.

0:12:41.180000 --> 0:12:43.720000
 So let's just pick something
 random here.

0:12:43.720000 --> 0:12:47.280000
 Let's go to, let's do this.

0:12:47.280000 --> 0:12:52.940000
 Basic HTML example.

0:12:52.940000 --> 0:13:00.860000
 Okay. So let's try this
 one right here.

0:13:00.860000 --> 0:13:02.680000
 SheldonBrown.com.

0:13:02.680000 --> 0:13:06.480000
 So I'm going to go ahead
 and start up my sniffer.

0:13:06.480000 --> 0:13:14.800000
 Paste and go. There we go.

0:13:14.800000 --> 0:13:17.260000
 Let's stop the sniffer.

0:13:17.260000 --> 0:13:25.300000
 Okay so what we should see here is somewhere
 in here we should see a DNS

0:13:25.300000 --> 0:13:32.260000
 resolution. Here we go.

0:13:32.260000 --> 0:13:34.860000
 Doing a standard query
 for an A record.

0:13:34.860000 --> 0:13:36.860000
 Let me open this up a little bit.

0:13:36.860000 --> 0:13:41.020000
 So here's UDP port
 53 which is DNS.

0:13:41.020000 --> 0:13:43.440000
 It's a DNS query.

0:13:43.440000 --> 0:13:48.100000
 And here in the query I'm saying I
 would like the A record which is an

0:13:48.100000 --> 0:13:55.500000
 IPv4 address for the website
 of SheldonBrown.com.

0:13:55.500000 --> 0:14:00.980000
 And then at some point I should
 get a response back.

0:14:00.980000 --> 0:14:08.260000
 Here it is. So frame number
 50 is a response back.

0:14:08.260000 --> 0:14:11.000000
 And it says here is the answer.

0:14:11.000000 --> 0:14:14.740000
 It says actually that IP address, that
 website maps to several different

0:14:14.740000 --> 0:14:20.860000
 IP addresses. So it must be hosted
 on more than one server.

0:14:20.860000 --> 0:14:26.740000
 All right so that is
 the DNS response.

0:14:26.740000 --> 0:14:30.900000
 And so then I start right here.

0:14:30.900000 --> 0:14:32.580000
 I start my TCP process.

0:14:32.580000 --> 0:14:37.920000
 So what I'm going to do is I'm going
 to select that frame and then I'm

0:14:37.920000 --> 0:14:42.860000
 going to right click and I'm going
 to do follow TCP stream.

0:14:42.860000 --> 0:14:44.420000
 Follow TCP stream.

0:14:44.420000 --> 0:14:48.160000
 That way I can only see that TCP stream
 and it will preclude all the other

0:14:48.160000 --> 0:14:51.780000
 jubilant. That wire sharp happened to
 pick up while I was doing that sniffer

0:14:51.780000 --> 0:15:00.620000
 capture. Okay. Well we see the
 sync, the syn, the TCP syn.

0:15:00.620000 --> 0:15:02.380000
 So this is a three way
 handshake right here.

0:15:02.380000 --> 0:15:05.860000
 The syn, the syn, ACK and the ACK.


0:15:05.860000 --> 0:15:07.280000
 But then we don't see
 the rest of it.

0:15:07.280000 --> 0:15:11.500000
 So I'm guessing that it probably
 changed over to HTTPS.

0:15:11.500000 --> 0:15:16.140000
 Let's find out. So the third step in
 the TCP three way handshake was frame

0:15:16.140000 --> 0:15:23.940000
 number 60. So let's go back
 to viewing all of it.

0:15:23.940000 --> 0:15:35.820000
 Let's see here. So
 that was number 60.

0:15:35.820000 --> 0:15:48.000000
 It's 196. Okay. Here is frame 62.

0:15:48.000000 --> 0:15:55.980000
 Okay. Well no, it's
 port number 80.

0:15:55.980000 --> 0:15:57.900000
 So that is HTTP.

0:15:57.900000 --> 0:16:04.160000
 Okay. But this is just a syn.

0:16:04.160000 --> 0:16:11.640000
 So this is still just a, looks like I tried
 to reach it via several different

0:16:11.640000 --> 0:16:16.400000
 ways. So DNS standard query response
 that's frame number 68.

0:16:16.400000 --> 0:16:18.340000
 Oh, where are we?

0:16:18.340000 --> 0:16:22.140000
 We want to get some
 HTTP going here.

0:16:22.140000 --> 0:16:30.940000
 Well, this is as I, okay,
 well here's one.

0:16:30.940000 --> 0:16:34.120000
 Here's an HTTP message.

0:16:34.120000 --> 0:16:38.100000
 So underneath my TCP is the
 hypertext transfer protocol.

0:16:38.100000 --> 0:16:43.000000
 If I open that up, you can see I'm sending
 a get request and saying, please

0:16:43.000000 --> 0:16:48.040000
 give, give me the web page that has
 this name, web underscore sample one

0:16:48.040000 --> 0:16:54.560000
 dot HTML. And it says, I prefer to
 use HTTP version one dot one and a

0:16:54.560000 --> 0:17:00.780000
 slash R and a slash N indicates
 a new line saying, I'm done.

0:17:00.780000 --> 0:17:02.180000
 I'm going to give you a new line.

0:17:02.180000 --> 0:17:06.400000
 And then the new line is, okay,
 I want Sheldon Brown dot com.

0:17:06.400000 --> 0:17:08.260000
 I want to keep alive.

0:17:08.260000 --> 0:17:10.960000
 And so you can see in my get request,
 there's a whole bunch of stuff here

0:17:10.960000 --> 0:17:14.580000
 that HTTP is indicating to the server
 saying, this is how I'd like to

0:17:14.580000 --> 0:17:26.940000
 talk to you. Response
 and frame 162.

0:17:26.940000 --> 0:17:38.820000
 All right. And we can see this
 is pretty small, right?

0:17:38.820000 --> 0:17:40.340000
 It's only 74 bytes.

0:17:40.340000 --> 0:17:41.480000
 You're under length.

0:17:41.480000 --> 0:17:43.160000
 But the next one.

0:17:43.160000 --> 0:17:46.480000
 So this is from 104 dot 18.

0:17:46.480000 --> 0:17:51.040000
 Where's the next one from that?

0:17:51.040000 --> 0:18:02.420000
 Here we go. So here frame
 number 183, 104 dot 18.

0:18:02.420000 --> 0:18:06.520000
 So this is from the server coming
 back to me much larger.

0:18:06.520000 --> 0:18:08.620000
 Well, no, it's only 54 bytes.

0:18:08.620000 --> 0:18:10.240000
 Not a whole lot in here.

0:18:10.240000 --> 0:18:13.620000
 This is only an ACK.

0:18:13.620000 --> 0:18:20.740000
 Well, unfortunately, this
 isn't HTTP get HTTP.

0:18:20.740000 --> 0:18:31.260000
 All right. Well, this isn't showing
 us as much as I had hoped.

0:18:31.260000 --> 0:18:36.600000
 But you get the general idea, which
 is that we had to do DNS first to

0:18:36.600000 --> 0:18:39.000000
 resolve the name to an IP address.


0:18:39.000000 --> 0:18:42.920000
 And then we're using HTTP to send a
 get message to the server saying,

0:18:42.920000 --> 0:18:44.280000
 this is what I want.

0:18:44.280000 --> 0:18:50.680000
 And then the server sends
 an OK message back.

0:18:50.680000 --> 0:18:52.140000
 And OK, here's an example.

0:18:52.140000 --> 0:18:55.040000
 So here in the response from the server,
 he's saying, OK, I'm giving you

0:18:55.040000 --> 0:18:58.520000
 a GIF. Here's a GIF image.

0:18:58.520000 --> 0:19:03.160000
 And here in it's giving us all sorts
 of information about the size of

0:19:03.160000 --> 0:19:08.860000
 the GIF, some of the background colors,
 the color map that's being used,

0:19:08.860000 --> 0:19:13.920000
 the position of where it's going
 to be on the website itself.

0:19:13.920000 --> 0:19:19.920000
 So all of this is being contained within
 HTTP to transfer this information

0:19:19.920000 --> 0:19:24.540000
 about the website back to me.

0:19:24.540000 --> 0:19:27.880000
 So some basic troubleshooting
 of HTTP.

0:19:27.880000 --> 0:19:31.120000
 Clearly, if you don't have any internet
 connectivity at all, you're not

0:19:31.120000 --> 0:19:33.260000
 going to be able to
 reach any websites.

0:19:33.260000 --> 0:19:38.140000
 Possibly the DNS server
 is unreachable.

0:19:38.140000 --> 0:19:44.140000
 An indication of this would be, you
 know, when you do a DNS resolution,

0:19:44.140000 --> 0:19:47.160000
 your laptop actually caches
 that information.

0:19:47.160000 --> 0:19:51.460000
 So if your laptop is open for several
 hours today and you go back to Google

0:19:51.460000 --> 0:19:56.760000
.com, you are not going to have to do
 a DNS resolution every single time,

0:19:56.760000 --> 0:19:58.540000
 you type in Google.com.

0:19:58.540000 --> 0:20:01.700000
 You'll do a DNS resolution the first time
 and then your laptop will probably

0:20:01.700000 --> 0:20:04.440000
 cache that for several hours.

0:20:04.440000 --> 0:20:09.140000
 And so if the DNS server becomes unreachable,
 an indication of that might

0:20:09.140000 --> 0:20:13.460000
 be that some of the websites you can
 get to, which are websites that you

0:20:13.460000 --> 0:20:17.360000
 were already looking at earlier today,
 that you already had cached in

0:20:17.360000 --> 0:20:21.640000
 your laptop, but new websites you're
 trying to bring up are unreachable

0:20:21.640000 --> 0:20:27.200000
 because you can't resolve those because
 the DNS server itself is unreachable.

0:20:27.200000 --> 0:20:31.120000
 Maybe the DNS server is unable to resolve
 the name, meaning, you know,

0:20:31.120000 --> 0:20:34.920000
 you mistyped in the name or you're typing
 the name of a web server that

0:20:34.920000 --> 0:20:36.580000
 no longer exists.

0:20:36.580000 --> 0:20:40.160000
 Maybe the actual website
 is unreachable.

0:20:40.160000 --> 0:20:44.500000
 The server that's hosting that website
 is, you know, we can't get to it.

0:20:44.500000 --> 0:20:47.660000
 Maybe the server itself is alive, but
 there's some router or switch or

0:20:47.660000 --> 0:20:53.440000
 something in between in the internet
 that is down or broken or not working

0:20:53.440000 --> 0:20:58.800000
 correctly. Or maybe the remote server
 itself is actually just down.

0:20:58.800000 --> 0:21:04.080000
 So these are all examples of some basic
 troubleshooting you can do with

0:21:04.080000 --> 0:21:07.460000
 websites and web browsing.

0:21:07.460000 --> 0:21:11.000000
 So that concludes this
 particular section.

0:21:11.000000 --> 0:21:14.740000
 And in the last video, I'm going
 to talk about how Telnet works.