Original subtitles

DNS services.

Hi, guys.

So in this lesson, we're going to learn about DNS services.

So I want to get right to it.

So DNS, as you may know, maybe you don't know it's an abbreviation of domain name system.

Yeah, that's all.

So it's basically a phonebook of the whole internet.

Yeah, it'll convert.

Easy to remember names like YouTube.com into IP addresses, for instance.

Two zero eight eight six five eight one five three eight two three eight.

OK, so DNS is a system used to convert hostnames up to 256 characters into that previously mentioned

IP address.

So the hostname, it's also known as the fully qualified name.

It indicates both the computer's name and the internet domain that the computer is in.

So DNS will resolve the IP address of a given machine name.

And it allows machines to communicate with other host names on the internet.

So then what's the purpose of death?

Well, I'm glad you asked, because the purpose of DNS is extremely simple.

It'll provide two sided conversion between easily understandable and usable machine and domain names

and machine IP addresses.

So since it's not practical to use them, remember IP addresses in daily life, who even remembers what

phone numbers are anymore?

The domain name system is used.

So the main purpose is to respond to inquiries about the domain name or IP number that's coming over

the network and for this purpose, the Berkeley Internet named Domain, or BND.

This is a software that gets widely used.

So when you want to access a site, DNS determines which site is where, which IP belongs, to which

computer, and then you can access the desired location.

Yeah.

So how does DNS work?

Well, the DNS system consists of name servers and resolvers, so computers are organized as name servers.

These whole IP addresses as information and they correspond to host names.

The resolvers are DNS clients, so DNS clients contain the addresses of the DNS server or servers.

So when a DNS client wants to find the IP address for a computer's name, it refers to the name server.

The name server that is the DNS server sends the IP address corresponding to this name right to the

client.

And hooks it up if there is such a name in its database.

Now, records must be manually entered into the DNS database.

So firstly, I want to tell you, the internet addresses are actually separated by country.

So express in such is R and D and UK at the end of addresses that you're typically familiar with will

indicate the country where the uterus is located.

For example, TR denotes Turkey, the E Germany, UK, England.

Right now, a country prefix is not actually used for USA addresses because while the country that created

DNS and similar applications actually is the USA, so I guess that makes that exempt.

Hmm.

OK.

Never mind.

So after internet addresses are divided into countries, they are further divided in this subsections.

These are known as common.

Edu or Edu and Gov.

Right?

And org, you can often hear Georgia OAG, so these expressions correspond to top level domains in DNS.

So the top level domains are.

Com Indicates commercial establishments.

Edu indicates educational institutions.

Org indicates non-commercial, non-governmental institutions.

Net indicates networks.

It act as an internet backbone.

Gov indicates governmental institutions.

Mile indicates military establishments numb, indicates places where you can find phone numbers.

Bali.

Indicates places where reverse DNS queries can be made.

Now, field names are used in a structure called a tree structure, which branches out according to

a certain rule addresses in all countries connected to the internet, except for America.

USA.

End with ISO three one six six.

The country code of that country.

DNS zone files and record types.

The file types required for Dennis are named not boot.

So this file is the very first file read by the program when Dennis starts named not local.

And this file is a file called loopback, which is used to resolve the address of the machine itself,

named Dot S.A..

And this contains the addresses of the machines at the top level called root server named not hosts.

And this file is the file where the addresses of the machines in a subdomain running DNS are written.

That is the addresses of all computers working in your area that you are responsible for.

Name Dot Reverse.

So this file is used to convert the IP addresses contained in the name Dot host file that we explained

above to the names in the sheens and is also similar in structure to the named Dot local file.

Key words used in DNS files include Directory.

Oh, this is just the directory where the specified files will be found is given and kept and say.

Cash indicates the cash file.

Primary, this is the name of the main server, primary name server.

OK.

The basic information of the domain is located in here, and the program starts his search first from

this server.

Forwarders, if the machine is not found on the main server, well, it'll start searching on the servers

specified here.

Cereal.

So here's a serial number, and this number is incremented after each change is made of the fire.

Refresh, so here it specified how long it takes for the adjusted files to refresh themselves.

Retry.

Now here is specified for how long a search will be tried again or how many times.

Expire.

How much time is going to elapse before the search will be terminated?

TTL, also known as Time to Live, specifies that the cash can be kept for a specific period of time.

Name specifies the machine name data, specifies the IP number.

How about a little history?

So there is absolutely no such thing as DNS until 1984.

Until that year, name IP resolution was done with a text file co-hosts, so the names and IP addresses

of computers on the internet were manually recorded in this file.

Can you imagine each computer on the internet had a copy of this file when a computer wanted to reach

another computer?

It would examine this file if the file contained a record of that computer would then get its IP address

and hey, say hello, and then commence communication.

Now, in order for this system to work well, the contents of the host's file had to always be up to

date.

In order to achieve all that, copies were made periodically by connecting to Stanford University.

Yep, and, well, real close to Silicon Valley and USA, where the original fire was kept.

But as you can imagine, as a number of computers on the internet increased, both the size of this

file began to reach extraordinary dimensions and the connection of computers on the internet to be able

to copy the file began to lock the computers up in Stanford.

So another downside to using a single host file was all that.

Since computers are on the same level, it was necessary to ensure that a computer name does not have

a duplicate on that whole global internet web thing.

So because of these problems and others, internet authorities produced DNS in 1984.

So DNS both put the computer database into a distributed structure and provided a hierarchical structure

between computers, so they distributed database and DNS was provided as follows.

Computers were classified according to the institutions to which they belong.

For example, a DNS server machine responsible for Turkey kept the list of computers in Turkey that

not TR domain I mentioned earlier.

Therefore, it wasn't necessary to keep all the information of all the computers in the entire internet

in one place.

So there is common DNS server software.

So we talked about before the most widely used DNS server software is bind.

Then there's Microsoft DNS servers, there's power DNS as well as software with different platforms

and different qualities.

But considering the amount of data that they processed, they consume very little resources.

So in that way, even on a primitive server, the very old and low CPU power tens of thousands of DNS

zones can broadcast.

DNS domain name resolution.

So the process where DNS protocol is used the most is domain name resolution.

DNS is mostly used to find the IP addresses of a domain whose domain name is known, including the processes

that we're going to talk about later on in the videos.

So how is that process performed?

Well, I'll tell you what, let's examine it through this diagram.

Domain name resolution processes go through the following stages Are you ready?

So the user sends a request to the domain name from the client computer.

So as the client has sent a request to the domain name before this domain name and his IP address are

registered in the DNS cache on the client computer.

So this DNS cache is checked first for IP resolution.

So if there's a record in the cash and the detail or time to live determined by the DNS server has not

expired.

Well, that the IP addresses obtained and the request is sent to that IP address.

So if you're in widows, you can always view the DNS cache by typing IP config slash display DNS as

it command in the command console application.

Now, if the IP address of the domain name is not found in the cache or if the IP address is found,

but the detail has expired and the client looks at the host file located on the C drive in Windows System32

drivers ETSI.

And if the IP address of the domain name exists in this file and it will look for that IP address,

the request is sent.

So what happens if the client computer cannot find the information that it wants to in the host file?

Well, the request is then forwarded to this DNS server.

The DNS server directs a request to the root server, with the IP address registered as a forward address.

So these DNS servers are located in organizations called ISP or internet service providers.

You probably pay a monthly fee or something for those.

So the root server forwards this incoming request to TLD servers.

And it's the tele servers that forward the request to the appropriate SLV servers, the servers actually

communicate with each other until the correct servers found.

After the correct host computer is found, the IP address information is returned to the client via

the DNS server.

You follow.

So we've got some more here.

If a donor server registered on the client computer is not found, name resolution for Windows computers

again is resolved with Windows or Windows Internet name service servers using net bios or network basic

input output system names.

So net bios names are unique names of a maximum of 16 characters that are assigned to the computer.

When the Windows operating system was first installed.

So wins servers offer name resolution and enable client computers to find net bios, names of machines.

So after checking the found net bios, names and IP addresses, there'll be written into the wins servers.

When clients want to find the net bios name and IP address, they'll first look at their net bios name

cache.

If the requested information is found in the tidal period has not passed by, a request is sent to the

IP address.

If the requested information cannot be found in the cache or the time has elapsed, well, then a request

gets sent to the wind server registered on the client computer.

And then if the search information is found on the wind server, guess what, its return to the client,

if not well, requests are made to other wind servers.

And then if the client does not receive a response from any of the wind servers, then it will try to

find a client known as net bios by broadcasting a network broadcast message.

If this also fails, the client start searching for LM host files.

Yeah, so an Elmos hose file is just a simple text file used to resolve IP addresses of Windows computer

names.

So if there's a small and frequently changing network environment and Elmhurst file is placed on all

the computers on the network so that the computers can find those wins, servers reverse DNS resolution.

So reverse DNS resolution performs domain discovery from IP addresses.

Which is the reverse response of DNS resolution, right?

So then how is that process performed?

Well, this logic is similar to domain name resolution, but there are some cases that I do want to

bring your attention to.

IP addresses are not interdependent like domain names.

Like an example, CBS Dot Udemy Mi.com is a subdomain of Udemy dot com, you understand.

So these are going to be interdependent.

But 10.10 10.10 is an IP address and then dc-10 that ten point eleven is an IP address, but they are

not dependent on each other in terms of a domain name.

That is the 10.10 that 10.10 IP address may represent the Air Commodore, while the 10.10 ten point

eleven IP address may represent the baidu.com address, which is much different, right?

Completely different.

But that being the case, logically finding the IP address of a domain name requires examining all IP

addresses.

So that's going to be a costly process, wouldn't you think?

However, this problem has been resolved by RPA or RPA by taking the hierarchical structure of IP addresses

as well as their domain names.

So we're going to have a look at this diagram, and here we see a hierarchical structure.

And a field named Dot RPA has been added to TLD servers.

And look at this, in-dash addr has been added as a subdomain of this field.

So when IP addresses are to be found, just like domain names, Bali starts from the name and proceeds

down.

So when you follow this structure down, the process of accessing IP addresses and finding domain names

is a whole lot easier.

Now, another thing that we've got to be aware of is the process of naming IP addresses, according

to the hierarchy where the name Dot and Dash ADR dot RPA like f shouldn't.

So while the IP in the picture is one nine two two eight one five two zero one two zero, it's named

one to 0.2 0.1 five dot one nine zero dot in Dash Addr Dot, R-Pa.

According to the hierarchy.

Yeah.

So I'm glad you were with me on that one.

Anyway, that's it for this, so we've now learned about the purpose of dance, how DNS works, DNS

zone files, record types, keywords using DNS files.

You actually got a little history lesson about DNS and some common DNS server software.

DNS domain name resolution reverse DNS resolution.

Whoa, what a lot donuts.

So I'm sure you learned a lot.

I know you didn't get bored, right?

Because you want to move on to the next lesson.

I'll see you there.