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DNS services.
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Hi, guys.
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So in this lesson, we're going to learn about DNS services.
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So I want to get right to it.
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So DNS, as you may know, maybe you don't know it's an abbreviation of domain name system.
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Yeah, that's all.
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So it's basically a phonebook of the whole internet.
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Yeah, it'll convert.
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Easy to remember names like YouTube.com into IP addresses, for instance.
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Two zero eight eight six five eight one five three eight two three eight.
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OK, so DNS is a system used to convert hostnames up to 256 characters into that previously mentioned
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IP address.
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So the hostname, it's also known as the fully qualified name.
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It indicates both the computer's name and the internet domain that the computer is in.
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So DNS will resolve the IP address of a given machine name.
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And it allows machines to communicate with other host names on the internet.
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So then what's the purpose of death?
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Well, I'm glad you asked, because the purpose of DNS is extremely simple.
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It'll provide two sided conversion between easily understandable and usable machine and domain names
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and machine IP addresses.
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So since it's not practical to use them, remember IP addresses in daily life, who even remembers what
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phone numbers are anymore?
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The domain name system is used.
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So the main purpose is to respond to inquiries about the domain name or IP number that's coming over
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the network and for this purpose, the Berkeley Internet named Domain, or BND.
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This is a software that gets widely used.
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So when you want to access a site, DNS determines which site is where, which IP belongs, to which
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computer, and then you can access the desired location.
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Yeah.
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So how does DNS work?
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Well, the DNS system consists of name servers and resolvers, so computers are organized as name servers.
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These whole IP addresses as information and they correspond to host names.
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The resolvers are DNS clients, so DNS clients contain the addresses of the DNS server or servers.
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So when a DNS client wants to find the IP address for a computer's name, it refers to the name server.
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The name server that is the DNS server sends the IP address corresponding to this name right to the
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client.
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And hooks it up if there is such a name in its database.
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Now, records must be manually entered into the DNS database.
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So firstly, I want to tell you, the internet addresses are actually separated by country.
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So express in such is R and D and UK at the end of addresses that you're typically familiar with will
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indicate the country where the uterus is located.
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For example, TR denotes Turkey, the E Germany, UK, England.
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Right now, a country prefix is not actually used for USA addresses because while the country that created
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DNS and similar applications actually is the USA, so I guess that makes that exempt.
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Hmm.
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OK.
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Never mind.
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So after internet addresses are divided into countries, they are further divided in this subsections.
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These are known as common.
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Edu or Edu and Gov.
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Right?
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And org, you can often hear Georgia OAG, so these expressions correspond to top level domains in DNS.
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So the top level domains are.
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Com Indicates commercial establishments.
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Edu indicates educational institutions.
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Org indicates non-commercial, non-governmental institutions.
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Net indicates networks.
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It act as an internet backbone.
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Gov indicates governmental institutions.
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Mile indicates military establishments numb, indicates places where you can find phone numbers.
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Bali.
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Indicates places where reverse DNS queries can be made.
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Now, field names are used in a structure called a tree structure, which branches out according to
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a certain rule addresses in all countries connected to the internet, except for America.
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USA.
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End with ISO three one six six.
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The country code of that country.
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DNS zone files and record types.
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The file types required for Dennis are named not boot.
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So this file is the very first file read by the program when Dennis starts named not local.
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And this file is a file called loopback, which is used to resolve the address of the machine itself,
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named Dot S.A..
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And this contains the addresses of the machines at the top level called root server named not hosts.
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And this file is the file where the addresses of the machines in a subdomain running DNS are written.
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That is the addresses of all computers working in your area that you are responsible for.
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Name Dot Reverse.
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So this file is used to convert the IP addresses contained in the name Dot host file that we explained
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above to the names in the sheens and is also similar in structure to the named Dot local file.
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Key words used in DNS files include Directory.
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Oh, this is just the directory where the specified files will be found is given and kept and say.
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Cash indicates the cash file.
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Primary, this is the name of the main server, primary name server.
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OK.
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The basic information of the domain is located in here, and the program starts his search first from
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this server.
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Forwarders, if the machine is not found on the main server, well, it'll start searching on the servers
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specified here.
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Cereal.
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So here's a serial number, and this number is incremented after each change is made of the fire.
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Refresh, so here it specified how long it takes for the adjusted files to refresh themselves.
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Retry.
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Now here is specified for how long a search will be tried again or how many times.
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Expire.
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How much time is going to elapse before the search will be terminated?
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TTL, also known as Time to Live, specifies that the cash can be kept for a specific period of time.
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Name specifies the machine name data, specifies the IP number.
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How about a little history?
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So there is absolutely no such thing as DNS until 1984.
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Until that year, name IP resolution was done with a text file co-hosts, so the names and IP addresses
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of computers on the internet were manually recorded in this file.
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Can you imagine each computer on the internet had a copy of this file when a computer wanted to reach
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another computer?
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It would examine this file if the file contained a record of that computer would then get its IP address
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and hey, say hello, and then commence communication.
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Now, in order for this system to work well, the contents of the host's file had to always be up to
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date.
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In order to achieve all that, copies were made periodically by connecting to Stanford University.
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Yep, and, well, real close to Silicon Valley and USA, where the original fire was kept.
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But as you can imagine, as a number of computers on the internet increased, both the size of this
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file began to reach extraordinary dimensions and the connection of computers on the internet to be able
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to copy the file began to lock the computers up in Stanford.
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So another downside to using a single host file was all that.
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Since computers are on the same level, it was necessary to ensure that a computer name does not have
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a duplicate on that whole global internet web thing.
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So because of these problems and others, internet authorities produced DNS in 1984.
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So DNS both put the computer database into a distributed structure and provided a hierarchical structure
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between computers, so they distributed database and DNS was provided as follows.
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Computers were classified according to the institutions to which they belong.
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For example, a DNS server machine responsible for Turkey kept the list of computers in Turkey that
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not TR domain I mentioned earlier.
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Therefore, it wasn't necessary to keep all the information of all the computers in the entire internet
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in one place.
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So there is common DNS server software.
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So we talked about before the most widely used DNS server software is bind.
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Then there's Microsoft DNS servers, there's power DNS as well as software with different platforms
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and different qualities.
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But considering the amount of data that they processed, they consume very little resources.
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So in that way, even on a primitive server, the very old and low CPU power tens of thousands of DNS
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zones can broadcast.
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DNS domain name resolution.
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So the process where DNS protocol is used the most is domain name resolution.
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DNS is mostly used to find the IP addresses of a domain whose domain name is known, including the processes
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that we're going to talk about later on in the videos.
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So how is that process performed?
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Well, I'll tell you what, let's examine it through this diagram.
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Domain name resolution processes go through the following stages Are you ready?
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So the user sends a request to the domain name from the client computer.
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So as the client has sent a request to the domain name before this domain name and his IP address are
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registered in the DNS cache on the client computer.
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So this DNS cache is checked first for IP resolution.
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So if there's a record in the cash and the detail or time to live determined by the DNS server has not
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expired.
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Well, that the IP addresses obtained and the request is sent to that IP address.
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So if you're in widows, you can always view the DNS cache by typing IP config slash display DNS as
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it command in the command console application.
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Now, if the IP address of the domain name is not found in the cache or if the IP address is found,
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but the detail has expired and the client looks at the host file located on the C drive in Windows System32
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drivers ETSI.
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And if the IP address of the domain name exists in this file and it will look for that IP address,
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the request is sent.
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So what happens if the client computer cannot find the information that it wants to in the host file?
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Well, the request is then forwarded to this DNS server.
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The DNS server directs a request to the root server, with the IP address registered as a forward address.
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So these DNS servers are located in organizations called ISP or internet service providers.
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You probably pay a monthly fee or something for those.
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So the root server forwards this incoming request to TLD servers.
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And it's the tele servers that forward the request to the appropriate SLV servers, the servers actually
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communicate with each other until the correct servers found.
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After the correct host computer is found, the IP address information is returned to the client via
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the DNS server.
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You follow.
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So we've got some more here.
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If a donor server registered on the client computer is not found, name resolution for Windows computers
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again is resolved with Windows or Windows Internet name service servers using net bios or network basic
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input output system names.
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So net bios names are unique names of a maximum of 16 characters that are assigned to the computer.
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When the Windows operating system was first installed.
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So wins servers offer name resolution and enable client computers to find net bios, names of machines.
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So after checking the found net bios, names and IP addresses, there'll be written into the wins servers.
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When clients want to find the net bios name and IP address, they'll first look at their net bios name
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cache.
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If the requested information is found in the tidal period has not passed by, a request is sent to the
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IP address.
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If the requested information cannot be found in the cache or the time has elapsed, well, then a request
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gets sent to the wind server registered on the client computer.
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And then if the search information is found on the wind server, guess what, its return to the client,
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if not well, requests are made to other wind servers.
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And then if the client does not receive a response from any of the wind servers, then it will try to
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find a client known as net bios by broadcasting a network broadcast message.
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If this also fails, the client start searching for LM host files.
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Yeah, so an Elmos hose file is just a simple text file used to resolve IP addresses of Windows computer
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names.
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So if there's a small and frequently changing network environment and Elmhurst file is placed on all
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the computers on the network so that the computers can find those wins, servers reverse DNS resolution.
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So reverse DNS resolution performs domain discovery from IP addresses.
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Which is the reverse response of DNS resolution, right?
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So then how is that process performed?
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Well, this logic is similar to domain name resolution, but there are some cases that I do want to
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bring your attention to.
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IP addresses are not interdependent like domain names.
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Like an example, CBS Dot Udemy Mi.com is a subdomain of Udemy dot com, you understand.
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So these are going to be interdependent.
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But 10.10 10.10 is an IP address and then dc-10 that ten point eleven is an IP address, but they are
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not dependent on each other in terms of a domain name.
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That is the 10.10 that 10.10 IP address may represent the Air Commodore, while the 10.10 ten point
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eleven IP address may represent the baidu.com address, which is much different, right?
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Completely different.
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But that being the case, logically finding the IP address of a domain name requires examining all IP
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addresses.
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So that's going to be a costly process, wouldn't you think?
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However, this problem has been resolved by RPA or RPA by taking the hierarchical structure of IP addresses
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as well as their domain names.
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So we're going to have a look at this diagram, and here we see a hierarchical structure.
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And a field named Dot RPA has been added to TLD servers.
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And look at this, in-dash addr has been added as a subdomain of this field.
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So when IP addresses are to be found, just like domain names, Bali starts from the name and proceeds
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down.
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So when you follow this structure down, the process of accessing IP addresses and finding domain names
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is a whole lot easier.
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Now, another thing that we've got to be aware of is the process of naming IP addresses, according
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to the hierarchy where the name Dot and Dash ADR dot RPA like f shouldn't.
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So while the IP in the picture is one nine two two eight one five two zero one two zero, it's named
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one to 0.2 0.1 five dot one nine zero dot in Dash Addr Dot, R-Pa.
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According to the hierarchy.
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Yeah.
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So I'm glad you were with me on that one.
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Anyway, that's it for this, so we've now learned about the purpose of dance, how DNS works, DNS
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zone files, record types, keywords using DNS files.
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You actually got a little history lesson about DNS and some common DNS server software.
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DNS domain name resolution reverse DNS resolution.
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Whoa, what a lot donuts.
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So I'm sure you learned a lot.
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I know you didn't get bored, right?
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Because you want to move on to the next lesson.
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I'll see you there.
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