All language subtitles for Free-CCNA-DNS-Day-38-CCNA-200-301-Complete-Course_en

This is a free, complete course for the CCNA.

If you like these videos, please subscribe\n

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In this video we will cover DNS, Domain Name\nSystem.

DNS is a protocol that you certainly make\n

DNS is all about making it easier for us humans\n

For example it allows us to use the domain\n

of having to enter an IP address.

Names like ‘youtube.com’ or ‘google.com’\n

DNS is part of exam topic 4.3, which says\n

You don’t need to know DNS in depth for\n

operations of DNS, just understand its basic\npurpose.

The information I give you in this video should\n

DNS-related questions on the CCNA exam.

Here’s what we’ll cover in this video.

I already mentioned it, but I’ll explain\na little more.

Then the basic functions of DNS, a quick overview\n

As I said before, I won’t get into unnecessary\n

Finally, I’ll show how to configure DNS\nin Cisco IOS.

Watch until the end of the video for a bonus\n

ExSim practice exams simulate the style and\n

other practice exams, and from personal experience\n

If you want to get ExSim, follow the link\n

Let’s review the purpose of DNS.

DNS is used to resolve human-readable names,\n

Resolve in this case means convert.

You enter a name, such as google.com, and\n

Machines such as PCs don’t use names, they\n

However names are much easier for us humans\n

IP addresses are human-readable too, of course.

IPv4 addresses especially aren’t too long\n

no doubt that names are much easier to remember.

What’s the IP address of youtube.com?

Thanks to DNS, you can access youtube.com\n

When you type ‘youtube.com’ into a web\n

for the IP address of youtube.com.

The DNS server, or servers, your device uses\n

DHCP is the dynamic host configuration protocol,\n

Okay, that’s the basic outline of DNS.

Now I’ll use this network to demonstrate\nhow it works.

Three PCs are connected to R1 via SW1.

R1 is connected to the Internet, and somewhere\n

So, let’s go on to PC1, a Windows PC, and\n

Here’s the CLI of PC1, the Windows command\nprompt.

I used the command IPCONFIG /ALL to display\n

You should remember this command, ‘verify\n

I’ll probably make a separate video to cover\n

So, here’s some of the information displayed.

Note that there is also the command IPCONFIG\n

what I want to show you, which is the DNS\n

As I said in the previous slide, end hosts\n

server to use via the protocol DHCP.

However we haven’t covered that yet in the\n

I used the command NSLOOKUP youtube.com.

I briefly showed you the NSLOOKUP command\n

It tells the device to ask its DNS server\n

As we saw before, PC1 is using Google’s\nDNS server at 8.8.8.8.

Here’s the answer from Google’s DNS server.

Youtube.com’s IPv4 address is 172.217.25.110,\n

So I tried a ping, specifying the name instead\nof IP address.

The name ‘youtube.com’ is then converted\n

Note that you don’t have to use the NSLOOKUP\n

If your device doesn’t know the correct\n

I just used NSLOOKUP to demonstrate the command.

To learn the IP address of youtube.com, PC1\n

Then the DNS server replies, telling PC1 that\n

What’s the role of R1 in this exchange?

In this case, R1 isn’t acting as a DNS server\nor client.

It is simply forwarding packets.

So, no DNS configuration is required on R1.

Often there’s simply no need to do any DNS\n

They just need to perform their job of routing\nnetwork traffic.

However, a Cisco router can act as a DNS server\n

I used Wireshark to capture the traffic from\n

It’s from source 192.168.0.101, PC1, to\n

Under ‘info’ it says standard query, so\n

Notice this part here, ‘A youtube.com’.

I’ll tell you in a minute what that ‘A’\nmeans.

Here’s the next message, from Google’s\n

Under ‘info’ it says standard query response.

So this is a response to PC1’s query.

And here it says A youtube.com A 172.217.25.110.

Notice that it’s an IPv4 address.

Now here’s the next message, again a standard\n

This time it says AAAA, which we call quadruple\nA, youtube.com.

And here’s the standard query response.

Quadruple A youtube.com, quadruple A, followed\n

So, can you guess what ‘A’ and ‘quadruple\nA’ stand for?

DNS ‘A’ records are used to map names\nto IPv4 addresses.

In the first query message, PC1 asked the\n

so the DNS server responded with an IPv4 address.

DNS ‘quadruple A’ records are used to\n

In the second query message, PC1 asked the\n

so the server responded with an IPv6 address.

Now let’s briefly look inside of that first\nquery.

Here’s Layer 4, which protocol is used?

Remember, DNS uses both TCP and UDP, so why\nis UDP used here?

Standard DNS queries and responses typically\nuse UDP.

TCP is used for DNS messages greater than\n512 bytes.

In either case, UDP or TCP, the port number\nis 53.

You don’t have to know the details of when\n

DNS queries and responses like these will\n

If you’d like to know the details, try a\n

Finally, down here is the UDP query itself,\n

As I’ve said before, Wireshark is a very\n

also has many real-world on-the-job uses.

If you have some time I recommend downloading\n

your computer is sending and receiving.

Moving on, let me introduce the DNS cache.

Devices will save the DNS server’s responses\n

This means they don’t have to query the\n

This saves a lot of unnecessary network traffic.

So, to view the DNS cache on a Windows PC\n

Here’s the record for youtube.com.

However look at the record type.

It’s not A or quadruple A, it’s CNAME,\n

CNAME, canonical name, is another kind of\n

I looked in the DNS cache for that other domain\n

same IPv4 address, 172.217.25.110.

So, as you can see there are some complexities\nto DNS.

DNS is a very important part of the Internet\n

for the CCNA you just need to know the basics.

Here’s one more command in the Windows command\n

It says the DNS resolver cache was flushed,\n

If I try to access youtube.com again, for\n

query to the DNS server to learn the IP address\nagain.

Before moving on to R1, here’s one more\npoint about these PCs.

In addition to a DNS cache, most devices have\n

In Windows it’s in the C:\\Windows\\System32\\drivers\\etc\n

Let’s see what’s in that file.

By default there are no hosts listed, however\n

by typing the IP address, a space, and then\nthe host name.

I then returned to the command prompt and\n

R1 because it had an entry in its hosts file.

This isn’t DNS, it’s a simple alternative\nto DNS.

A long time ago before DNS was invented, host\n

In modern days a hosts file might be used\n

local network if necessary, however DNS is\n

Okay, so I hope that gave you a general understanding\n

A client wants to access something using a\n

But in order to access the website, it needs\n

To learn the IP address, the client sends\n

Now let’s look at how to configure DNS in\n

Let me repeat, for hosts in a network to use\n

They will simply forward the DNS messages\n

However, the Cisco router itself can be configured\n

If an internal DNS server is used, usually\n

By ‘internal’ I mean a DNS server in the\n

Also, a Cisco router can be configured as\n

other commands using names instead of IP addresses.

Here’s how to configure a router as a DNS\nserver.

First, you should use the command IP DNS SERVER\n

This configures the router to act as a DNS\nserver.

If a client sends a DNS query to R1, R1 will\n

However, for that to work R1 needs to have\nsome records.

Use the IP HOST command, followed by the host\n

I configured entries for R1 itself, PC1, PC2,\nand PC3.

Next, it’s a good idea to configure an external\n

R1 will query this server if it doesn’t\n

I configured R1 to use Google’s DNS server\nat 8.8.8.8.

I’ll demonstrate how this works in a minute.

The final command is IP DOMAIN LOOKUP.

This enables R1 to perform DNS queries.

If this command isn’t enabled, R1 won’t\n

However, this command is enabled by default,\n

By the way, a lot of resources teach an old\n

This is the old version of the command, however\n

You should probably know both versions, with\n

So, that’s how you configure a router to\nbe a DNS server.

Now let me demonstrate how it works.

So let’s say PC1 wants to ping PC2.

By the way, I configured PC1 to use R1 as\n

So I issue the PING PC2 command on PC1, however\n

only a single ping, for the purpose of this\ndemonstration.

PC1 doesn’t have an entry for PC2 in its\n

It sends a query to its DNS server R1, asking\n

R1 has an entry for PC2, I just configured\n

Finally PC1 sends the ping to PC2, PC2 sends\n

Now PC1 has entry for PC2 in its DNS cache,\n

won’t have to perform a DNS query, it already\n

Okay I’ve added the YouTube server to the\ndiagram.

This time, I issued the command PING YOUTUBE.COM\n-N 1.

So let me walk through that process again.

Before PC1 can actually send the ping, it\n

so it sends a query to its DNS server, R1.

However, R1 doesn’t have an entry for youtube.com.

Remember I used the IP NAME-SERVER 8.8.8.8\n

That’s what it does, it sends a DNS query\nto 8.8.8.8.

Google’s server replies, telling R1 the\n

Now R1 is able to reply to PC1’s query,\n

Finally PC1 is able to send the ping to YouTube,\n

Sorry for the messy diagram, but I hope that\n

R1 acts as a DNS server for PC1, but if it\n

PC1 requests, it acts as a DNS client and\n

To view both the configured hosts, as well\n

For example, here you can see the cached entry\n

Notice in the ‘flags’ column it says ‘temp’,\nfor temporary.

Because this entry was learned via DNS it\nis not permanent.

If it expires it will have to be re-learned.

These manually configured entries, however,\n

Next, here’s how to configure a Cisco router\nas a DNS client.

Basically, two of the commands I already showed\n

So, to demonstrate this I deleted all DNS\nsettings from R1.

Then I tried to ping youtube.com, but it didn’t\nwork.

R1 wasn’t able to translate ‘youtube.com’\nto an IP address.

Then I used the command IP NAME-SERVER 8.8.8.8,\n

I also used the command IP DOMAIN LOOKUP.

Once again, this command is enabled by default\n

Then I tried the ping again and it worked.

So, we have configured R1 as a DNS client.

However, this time it is not a DNS server.

If PC1 tries to use R1 as a DNS server, R1\n

Now there is one more optional command that\nyou can use.

That is the IP DOMAIN NAME command, I specified\n

You’ve probably heard the term ‘domain’\n

I’ve mentioned it a few times in this video.

Names like ‘google.com’ and ‘jeremysitlab.com’\n

or area of administrative control in the Internet.

For example, the domain name ‘google.com’\n

this server ’dns.google.com’, Google’s\n

under Google’s administration and control.

When this command is applied, this will be\n

without a specified domain name.

For example, the command PING PC1 will actually\n

Like the IP DOMAIN LOOKUP command, there is\n

That old version is still supported in modern\n

I will cover this command in a later video\nabout SSH.

SSH is a protocol that can be used to connect\n

a domain name is needed to enable SSH.

I’ll cover this command more in that video.

For review, here are the commands I showed\n

use in the Windows command prompt and the\nCisco IOS commands.

If you don’t remember any of these commands,\n

Before moving on to the quiz, let’s review\n

First I introduced the purpose of DNS.

Basically it enables the use of easy-to-remember\n

DNS clients send queries to DNS servers, asking\n

youtube.com, and the server replies, telling\nit the IP address.

Then I demonstrated some of the basic functions\n

I showed how it used Google’s DNS server\n

then it added that IP address to its own DNS\ncache.

Finally I showed you how to configure a Cisco\n

As I have already said multiple times, in\n

Usually you have a separate DNS server fill\nthat role.

However you still should know how to configure\nit.

Make sure to watch until the end of the quiz\n

ExSim for CCNA, the best practice exams for\nthe CCNA.

Okay, let’s go to question 1 of the quiz.

Which of the following Windows command prompt\n

Pause the video now to find the correct answers,\nselect two.

The correct answers are B, IPCONFIG /ALL and\nD, NSLOOKUP.

Both of these commands will show the DNS server\n

A, IPCONFIG displays things like the PC’s\n

but not details like the DNS server.

C, IPCONFIG /DISPLAYDNS shows the PC’s DNS\n

Although the CCNA is focused on the Cisco\n

operating systems is now a CCNA exam topic\n

Which of the following statements about DNS\n

Pause the video now to find the correct answers,\nselect two.

The correct answers are B and D. DNS ‘A’\n

And a Cisco router can be both a DNS server\n

A is incorrect because messages greater than\n

UDP is used for messages 512 bytes or less\nin size.

As for C, quadruple A records, not triple\n

PC1 is configured to use an external server,\n

What DNS command is necessary on R1 to enable\nthis?

Pause the video to think about the answer.

The answer is D. No DNS configurations are\nneeded on R1.

To forward DNS queries and replies between\n

It will simply forward the packets as normal.

Which of the following Cisco IOS commands\n

Pause the video to think about the answer.

It displays both the hosts learned via DNS\n

B and D are not real commands, and C is the\n

Okay, let’s go to question 5.

Which of the following protocols can hosts\n

Pause the video to think about your answer.

Dynamic Host Configuration Protocol allows\n

their IP address and subnet mask, default\n

DHCP will be covered in another video.

Okay, that’s all for the quiz.

Now let’s take a look at a bonus question\n

Okay here's today's Boson ExSim practice question.

A web browser on HostA sends an HTTP request\nto WWW_server.

This is the first time HostA has ever sent\n

HostA does not use a hosts files.

With which of the following devices does HostA\n

A, only DNS_server and WWW_server.

B, DNS_server, Default_GW, and WWW_server.

C, only Default_GW and WWW_server.

Okay pause the video now to find the correct\nanswer.

First, does HostA established a TCP connection\nwith Default_GW?

This router simply forwards traffic between\n

something on this router so there's no need\n

So it says this is the first time HostA has\n

So that means it has no entry in its DNS cache\n

And HostA also does not use a hosts file,\n

learn the IP address of the web server.

So, to learn the IP address from the DNS server,\n

Does it establish a TCP connection?

As I said in this video, standard DNS queries\n

So there's no need to establish a TCP connection\n

Finally, how about the web server?

Does it establish a TCP connection?

Yes, a web browser on HostA sends an HTTP\n

HTTP uses TCP port 80, so HostA must establish\n

So that means the answer is D, only WWW_server.

Click on show answer and there it is, correct.

So here is Boson's explanation.

You can pause the video to read it, and I\nrecommend you do.

They also have a reference to some documentation\n

Okay so that's Boson ExSim for the CCNA.

These are by far the best practice exams for\nthe CCNA.

If you want to get Boson ExSim, please follow\n

There are supplementary materials for this\nvideo.

There is a flashcard deck to use with the\nsoftware ‘Anki’.

There will also be a packet tracer practice\n

That will be in the next video.

Sign up for my mailing list via the link in\n

the flashcards and packet tracer lab files\nfor the course.

Before finishing today’s video I want to\n

To join, please click the ‘Join’ button\nunder the video.

Thank you to Donald, C Mohd, Gustavo, Anthony,\n

Justin, Prakaash, Nasir, Erlison, Apogee,\n

Velvijaykum, Mark, Yousif, Boson Software,\n

Sorry if I pronounced your name incorrectly,\n

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