>> Let's talk about network services.
The three main services we're going to focus
on in this section is going to be DNS,
Domain Naming service,
DHCP, Dynamic Host Configuration Protocol,
and then the last is IPM,
which is IP address management.
These are some services that
are important on the network.
Let's start with arguably the
most important service on the network.
Certainly one of them.
That's DNS.
We really have to appreciate with DNS does for us.
Because you and I are good with names,
but we're not good with IP addresses.
I'm going to assume that's the case.
Most of us appreciate a user friendly name.
I know how to go to amazon.com.
I've no clue what the IP address is,
but we have to remember when
hosts are making a network connection,
one of the things they need is an IP address.
That's a layer 3 resolution that has to happen.
It's DNS that we go to.
Our clients are configured to know who
their local DNS server is.
When there's any sort of
naming that's used for a connection,
the client immediately carries their local DNS server.
As long as that local DNS server
has the information stored,
then it responds with an IP address.
The client is then able to add that layer in
the layer 3 packet header
and we can make that connection.
That's assuming the local DNS server
has that information.
In a minute, we'll discuss what happens if
the local DNS server does not have that information.
At any rate, DNS is the information
>> stored in a database.
>> Today is a dynamic database
where hosts are able to update DNS,
perhaps if their name or IP address
changes as new hosts come on to the network.
They're are also able to register with DNS.
DNS is a lot easier to manage than it was years ago.
As a matter of fact, many years ago,
we used to have a static text file on
client systems called the hosts file.
That host file would be manually updated with
a user-friendly name and IP address.
DNS came along offering an automatic database.
As DNS involved, allowing host registered dynamically,
which is much easier than it used to be.
But it's really clerical service
and everything is based on the database.
The database contains a series of records.
I would definitely know these record types.
They come up multiple times on the exam.
The idea is that for specific queries,
specific records are used.
The one we think of most often when thinking
of DNS is an A record,
also known as host record. Other name is fine.
This is the record that takes
a known FQDN and resolves an IP address.
We connect to amazon.com and we get
an IP address that matches the server's name.
We can do that for local usage,
or as long as we're configured to use internet servers,
we can get name resolution and connect
to any server by name in the world as
long as we have DNS configured properly and
there are no issues with the server
>> to which we connect.
>> Name resolution is very important.
It's the host record we think about most
of the time that can be called the A record.
There's also a quad A record that's designed
for IPv6 to FQDN resolution.
The PTR record, Pointer record
is actually the opposite of a host record,
what it's going to do is if you have an IP address,
it will find the fully qualified domain name.
If you think, when am I going to find
the IP address and not know the name of the server?
This is something that's used by
a lot of tools on the network.
It's also used if you have anti-malware software.
You may get a notice that there's
a specific domain or host that
>> it's scanning your system.
>> That requires pointer resolutions
>> or reverse resolutions.
>> As a matter of fact, they call
the zone reverse lookup zone.
Whereas when you're using a host record,
that's a forward lookup.
There's a handful of others.
Start of Authority, SoA,
is the name server that's authoritative for the zone.
Your SoA is usually
the first DNS server that
has name resolution for that zone.
You may have another other name servers redundancy.
That's what the NS records are for.
The SRV or Service records
are really important because they
list the critical network services
>> in their IP addresses.
>> For instance, if your host needs to know where
a domain controller is, it asks DNS.
DNS uses the service record and says an LDAP server,
here's the IP address for it.
For our Kerberos Key Distribution agent server
or a global catalog server or mail server.
The service records have
all the services and which servers are running them.
There's also a record type called the
CNAME or an alias record.
If you want clients to connect to
a specific host and maybe
have a more professional name for the host.
But on the back-end, you want to name
it after some Star Trek character,
which invariably most of us in IT would want to have
our servers named after
Star Trek characters rather than www.
How boring is that? Well,
we know that our web browsers are going to
connect to a server, www.
We create an alias record
that says when they type out www,
send them to server Picard
or whoever your favorite character is.
I don't want to go down the nerd trail,
but I prefer to name mine after
>> Harry Potter characters.
>> No server named after he who must not be named,
hopefully not going to bring
the Voldemort server onto
the network. That doesn't bode well.
Finally, the last record type is the mail server.
An MX record that will
indicate where the mail servers are.
These records are really the heart and soul of DNS.
These are the records that are used
anytime you make a query to the DNS server.
The way DNS works is,
let's say that I'm trying to get
to google.com or something
that basic or the web server for google.com.
Even though we don't type out www anymore,
that's understood within the web browser.
I, as a client, type out,
www.google.com,
and I send a DNS query to my local DNS server.
It's called the DNS resolver.
Now because the google.com domain
isn't managed by my local DNS server,
my DNS server sends out some
curious to try to learn where the
>> server is looking for.
>> The first thing my local DNS server
does is it goes out to
the internet and contacts a route server.
There are multiple routes servers out on the Internet.
This is like the ultimate point of origin for DNS.
The DNS resolver says, "Hey, route,
do you happen to know where www.google.com is?"
The route says, "Nope, but I do know
where the.com server is."
My local DNS server then goes to
the top-level domain name server, .com in this case,
and says, "Hey, do you know where www.google.com is?"
The com server comes back and says,
"Nope, but I do know where the Google name server is."
My DNS server then sends a query to Google and says,
"Do you know where www.google.com is?"
Google says, "Yes, I do.
Here's the IP address for our web server."
That's passed back to my local DNS server,
who was the resolver,
who then passes it back to me as the client.
Now, I'm able to connect to Google's web server by IP.
Now, there are other ways to expedite this.
There's cash and there are
some other things you can configure.
But in and of itself,
this is the hierarchy that
DNS uses to provide name resolution.
Don't forget, DNS is really critical
on the network because in addition to name resolution,
it also tracks critical services
where your mail servers are.
It's needed for troubleshooting utilities.
DNS is really important.
It's a hierarchical database starting out at
the root with the top levels and then secondary levels.