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- [Instructor] Servers Part
3: DHCP and DNS Servers.

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The DHCP server is in charge

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of handing out IP addresses to clients.

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It also gives out additional
TCP/IP information.

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So here in our illustration

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we have a DHCP server

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here on the LAN,

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and normally this would
hand out the IP address

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to all the clients automatically.

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It would also hand out the subnet mask,

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gateway address and the IP
address of the DNS server.

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So this is very common

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and this could be a SOHO router
that runs as a DHCP server

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or it could be a Windows server
that hands out IP addresses.

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You could also have DHCP
servers on the internet.

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And, for example, let's
say had a small office

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or a home office,

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and you had your SOHO
router/firewall device.

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Well, in order for computers
that are connected to this

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to get out to the internet
and access websites,

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this device that SOHO router
needs to get an IP address

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from the DHCP server at the ISP,

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a public IP address that'll allow it

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to communicate on the internet.

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So two different types there.

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Now, let's focus on the
DHCP server on the LAN

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and we'll show some IP config
information on a client,

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and then we'll show two examples

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of DHCP servers on the local area network.

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We'll start here, this is a
Windows 7 Virtual Machine.

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So we'll run an IP config command

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to see the TCP/IP information.

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And we need to do that
with the /all option

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so that we can see all
the information here.

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We'll press enter.

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and here's our local area
connection, our ethernet adapter.

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And it says here DHCP is enabled, yes.

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So we know we're getting this information

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from a DHCP server.

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In this case, it's a virtual DHCP server.

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It actually comes from within VMware.

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Here's the IP address that I've
been given at this computer.

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Here's the subnet mask, triple 255.

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Here's the gateway address,

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and that is the virtual switch,

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the virtual router, actually in VMware,

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that's .2

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And the DHCP server is
actually known as .254,

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but that's kind of all built
into the virtual system.

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And DNS servers .2 over here.

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So that's a bunch of
information that you get

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from the DHCP server.

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You get your IP address, the subnet masks,

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the default gateway, and
the DNS server information.

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So let's show two
examples of DHCP servers.

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First here, we have a basic router

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and I've gone to advanced,
and I've gone to network,

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and DHCP server.

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And you can see that the
DHCP server is on right now,

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it is enabled.

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And we have an IP address Pool,

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otherwise known as a scope.

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And this server will hand out IP addresses

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to clients automatically
between 10.252.0.2

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and 10.252.255.254.

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And so this device is considered
to be the gateway .101.

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We don't have DNS servers
placed in here, so by default

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this would forward DNS
requests out to the internet.

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So it would be 101 automatically
at the client side.

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Now let's take a look at
another type of server.

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This is server 2012 that I have running.

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And I've set this up as a DHCP server

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which you have to add as
a role to Windows Server.

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So I've added that and
I'm in the DHCP console.

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And then within IPv4 and IPv6
you would create a new scope,

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which is a Pool of IP addresses.

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And so I've created that here,

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and we have 10.1.1.1. through 10.1.200.254

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using a 255.255 subnet mask.

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This is where you'd go to
create this scope of information

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and we'd add additional info,
like the gateway address

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and who the DNS server is.

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We do all that here, create
that scope, activate the scope

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and then authorize the server.

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And you wanna see a green
arrow pointing up on the server

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and on the scope to make sure
then verify that you know

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that your server is running properly.

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So two examples of servers there for DHCP.

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Now DHCP uses a four step process

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that we discussed in other videos,

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and that's called Dora,
D-O-R-A, which stands for

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Discover, Offer, Request,
and Acknowledgement.

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And that's generally what happens

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between clients and the server.

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The client will not have an IP
address and you might plug it

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into the network or enable
the wireless adapter

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and it'll look out to the network

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if it's set to obtain IP
addresses automatically.

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It'll look out to the network
to find a DHCP server.

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And that's part of the discovery
phase, that D within Dora.

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Once it finds one, the
server will have an offering.

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It'll do an offering to
the client of IP addresses.

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The client will request
one, quote/unquote,

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it'll request an IP address,

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which is really one that the
DHCP server decides for it.

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And if that's available and
the client meets the criteria

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the DHCP server will acknowledge that

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and the client can start
using that IP address.

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So that's the four step
process known as Dora.

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And that's a little
bit about DHCP servers.

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Remember they could be on the LAN

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handing out IPS to all the clients,

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or they could be out on the internet,

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handing out an IP address
that's publicly used to say

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your router or whatever
device that publicly

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faces the internet and allows
access out to the internet.

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Now, the domain name
system, or DNS server,

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resolves domain names to IP addresses.

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DNS is a system that
could be run on your LAN

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as part of your Windows
domain, but it is also

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a worldwide system that
translates all website

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domain names into their
corresponding IP addresses.

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So DNS servers could be on the LAN.

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They could be on the DMZ and
they're all over the internet.

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There's a whole hierarchy of
DNS servers around the world.

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Where your organization
places a DNS server

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will depend on several factors,

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namely what kind of other servers you have

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and who needs to access
them and from where.

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So for example, here, we have a DNS server

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in our local area network,
and that's possible.

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You might have this,

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especially if you have
an authentication server,

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if you're running say a Windows domain

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which we'll talk about
in a following video.

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And that would take care
of the name resolution

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for all the domain
information on your LAN.

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So that runs in conjunction, in concert,

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with the domain server, with
that authentication server.

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But they can also exist,
as say part of the DMZ,

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or on the internet.

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And they do the same thing.

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They're gonna resolve domain
names to IP addresses.

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So if a client wants to say, a
client that's on the internet

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wants to go to this web server here,

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that client might know the domain name,

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but they're probably not
gonna know the IP address,

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and that's how computers
communicate with each other.

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So the DNS server is
gonna be needed to resolve

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that domain name to IP,
to allow that connectivity

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between the web server and the client,

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wherever that client is on the internet.

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So you might have these DNS
servers just about anywhere.

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And again, there's a
whole hierarchy of these

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around the world.

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When you go to the internet
and try to connect to a domain

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it's gonna go to the initial DNS server.

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Let's show another example here.

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Okay, this is my Windows 10 system here.

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And so here we'll do another ipconfig/all.

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We get lots of information here

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and let's take a look at this,

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the main network ethernet adapter.

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This one's not using DHCP.

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I've statically configured the IP address.

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And when that's the case,

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we have to statically
configure everything else,

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the subnet mask, the gateway we're using

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and the DNS server.

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Now the DNS server is the gateway,

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it's the SOHO router that I'm using.

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But that gateway is gonna have
to look out to the internet

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to another DNS server when I
try to connect to domain names.

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So for example, if we were to do a ping

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to something like
example.com, my SOHO router

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is not gonna know the IP
address of example.com.

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It's gonna have to look
out to the DNS server.

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And the first place
it'll go to look for that

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is at my ISP, at my
internet service provider,

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their in-house DNS server or DNS servers.

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Hopefully they'll come back
with the IP address for that.

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And I just did a quick ping to show this.

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So example.com is using
this IP address right now.

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But it could be that they
don't know that server

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or maybe they know this server

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but the DNS servers at my
ISP don't know other servers.

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So for example, I could
do ping davidlprouse.com,

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maybe they don't know
that domain right now.

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They should by now, but
let's say they don't.

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Then that DNS server at
my IP would have to go out

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to another higher level DNS server

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somewhere else in the country.

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And if you want to connect
to other countries,

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your local DNS server would
forward the DNS requests

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to those other countries' DNS servers,

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and ultimately get the
IP address that you need.

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And whenever you're connecting
with your web browser

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that's actually what's happening.

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The IP address of your local computer

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or your SOHO router will
connect out to that IP address

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and they communicate directly via IP.

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Let's go back to our Server 2012 here

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and I'm going to go to the DNS manager.

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Now, well, first we'll go to
the Server Manager Dashboard.

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Now this particular server started

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as a basic file and
storage services server,

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but then I wanted to promote
it to a domain controller

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to become an authentication server.

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So we installed active
directory domain services.

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And to do that, we have to
point to some DNS server

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either a separate box,
or you could install it

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at this same server, which is what I did.

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I installed DNS here
and it's up and running.

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We got the green arrow pointing up.

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So that is running and to work with that,

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you can work within the
DNS manager console.

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And you can see here, we have
DNS and we have this computer.

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This is the fully qualified
domain name for this server.

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It's dc1, that's the name of the computer.

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The domain is dpro 42.com,

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which I selected when I installed DNS.

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And if we look here, we'll
see the forward lookup zones,

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and we have dpro42.com, and
you can see the resolutions

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that can be made from this computer,

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dc1 is also known as 10.252.0.103 and .105

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'cause it's a multi-homed server.

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And then other computers that connect,

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like say the Windows 10 laptop 1

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that we've connected to before

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that name will also
resolve to its IP address

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and that'll be added to the DNS manager.

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So anything that deals with this domain

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and all the post names within the domain

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will get added to this
forward lookup zone.

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And DNS can work in reverse as well.

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It can resolve from IP
address to domain name, right.

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So you have both of those
functions within DNS.

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And this is running within Server 2012.

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And this is one example of a DNS server

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that does this name resolution.

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Okay, so we have the DNS
servers here on the LAN

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and that's common if you have a domain

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and we'll talk more about that
with authentication servers.

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But more often what you're
looking at is the DNS server

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out on the internet, or on your DMZ,

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which takes care of the
resolutions between domain names

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and IP addresses,
especially for web servers

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but just about any
other servers out there.

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So you wanna know your DHCP
and your DNS functionality

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and the servers and where they might be

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and what they can do, DHCP
and DNS servers do things

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that happen behind the scenes,

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even more so than your typical server.

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Nevertheless, they are
vital to a network's smooth

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and automated operation.