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- [Instructor] Hi and
welcome back to the course.

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In this video, we're going to quickly look

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at how the Domain Name System works.

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In the left here in this
diagram we've got your browser

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and let's say you're
accessing example.com.

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Now, your browser doesn't know

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the IP address for example.com,

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so the first thing it
does is it checks to see

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if the operating system
knows the IP address.

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This can happen if you've
accessed it recently, for example.

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Now, if the operating
system knows the IP address,

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then that's fine, it
goes back to the browser

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and that'll loads the IP
address and all is good.

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However, normally the operating system

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won't know the IP address
for a given domain.

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So what happens is a DNS query begins.

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Now, the first thing that happens

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is because

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the domains are so numerous,

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there are so many domains
many millions of them,

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it is not a single server that tells you

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where the IP address
for a given domain is.

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So, it goes through a number of steps

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in trying to find out the IP address

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related to a single domain.

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The first thing that happens

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is we go to one of the root servers

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and these are hard-coded in
the internet provider's system.

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So, there are a few hundred root servers

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and when new root servers are added

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then all of the internet providers update

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and add the new root servers.

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And that doesn't happen that often.

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There's a number of companies
that manage the root servers

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and all is good.

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So, the first thing that happens
is we go to a root server

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and the root server will tell us,

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"I don't know anything about example.com

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"that's way too specific,
but I know about the .com."

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So, it'll tell us

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the IP addresses for the .com servers.

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Okay.

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So, then the browser is like,
"Okay, now I know .com."

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That's the first part of the address.

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That's the top-level domain,
a TLD commonly called.

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So, what it does is it then
goes to the .com servers.

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These are TLD servers and
these are also managed

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by specific organisations,

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I think Verisign is one
of the organisations

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that manages the .com domains.

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And it asks, "Okay, do you know anything

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"about "example.com's IP address?

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"What's the IP address of example.com?"

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And this TLD server will say,

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"I don't know the IP
address of example.com,

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"but I know the IP address of the server

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"that knows the IP
address of example.com."

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So, it gives (mumbles) of that.

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And then at the end, the last
step is to go to the server

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that knows the IP address and ask it,

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"What's the IP address of example.com?"

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And then, that tells us the
IP address of example.com,

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which is that down here,

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and the browser then
loads that IP address.

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So the first thing, is to
go to a root name server.

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That tells us the top-level
domain name servers.

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That tells us the
authoritative name servers.

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And that tells us the IP
address, which we then load.

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Going back to Cloudflare,

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what we've set up here
beth.ns.cloudflare.com

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and justin.ns.cloudflare.com,

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those are the authoritative name servers.

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So, those are the servers that know

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the IP address of example.com,

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or in our case restapicoursetrial.com.

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And in our DNS settings,
which we can go up here,

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we can go to the DNS settings,

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we have defined

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that IP address.

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Whenever we go to one of
those two name servers,

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they will know okay this A record exists,

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restapicoursetrial.com and they'll give

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the browser this IP address.

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Okay.

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So, that's how the Domain Name System,

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in a very simplified fashion, works.

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In the description of the lecture,

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I'm going to put a couple more links

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to see if you want more
info, you can go to that.

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But, next steps are to modify

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our DNS settings so they are correct,

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because right now they
are not really correct.

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We've got a bunch of
settings that we don't need,

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such as the MX settings,

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and we've got a bunch of
settings that are wrong,

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like the A and the C name records.

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So in the very next
video, let's change them

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and make sure they are correct

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and they are pointing to the right server.

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I'll see you in the very next video.