Earlier video, we talked about the domain name system process.
We talked about the servers that you would communicate to.
But we really didn't talk about the internals of those servers.
Those servers are running DNS software.
And that software has a number of records
that it uses to provide you with information about name servers
and IP addresses.
These are called resource records, or RR.
These are all of the different records
for all of those different devices
that you might run into.
And there are a lot of different record types.
There are over 30 record types.
Some of them will tell you about IP addresses.
Others tell you about certificates.
Others tell you about name servers, alias names,
and so much more.
And in this video, we'll step through what
some of the most used DNS records are.
If we were to log in to a DNS server
and look at its configuration, we
would find a forward lookup file that
looks something like this one.
You can see this is easy to read.
There are different sections.
And a lot of this may be pretty clear of what
it's trying to tell you.
Everything that we need to configure
is in this text file, which also makes
it very easy if we need to make a change to any
of these settings.
If we look a little closer at the configuration file,
we can see some comments, like a list of machine names
and addresses.
And these must be the machine spock.mydomain.name.
We have a Mail.
And we have a Kirk.
And we can see IP addresses that appear to be
associated with those as well.
And once we step through this, not only will
these names and IP address be clear to you,
but you'll also be able to figure out what everything
is in the middle, as well.
One of the most common records in a DNS
serve-- and, from our perspective,
one of the most important-- is the A record.
A stands for Address.
And this is how we ultimately define a name
with an IP address.
An A record is an IP version 4 address.
That as what we commonly will see and use on the internet,
although IP version 6, of course,
is becoming much more popular as of late.
So we have A records for IPv6, as well.
There are quad A records.
AAAA is what you will see in that DNS lookup file,
instead of just a simple A that designates IP version 4.
It's all in the same configuration file.
It's the same DNS server.
It's just a different record that we would put
inside of the server itself.
Here's an example of an A record that
might be for my web server.
So you have www.professormesser.com.
The IN stands for internet.
There's the A for the A record, which
means this must be an IP version 4 address.
And indeed, it is-- 162.159.246.164.
And there's a semicolon there to put some remarks
or different information in the file
so that you can remember what it is for later,
and to simply have my name right after that.
If there are other IP addresses and names
that you'd like to add, you simply add additional A records
to the file.
And that DNS server can now provide anybody
with information about these A records that you add.
The domain name system also allows
us to name a single device but give it multiple names.
Give it a nickname.
Give it a secondary name.
Add as many extra names as you would like.
And they can all associate back to one individual device.
And you can see an example of this
as something called a canonical name record, or CNAME.
This is something like gopher on the internet.
The CNAME is mail.domain.name.
But if I use FTP as the name, it also
refers to mail.mydomain.name.
And www also refers to mail.mydomain.name.
That way, we can have names that are familiar to people
and things that people can find easily, but point them all back
to a single server that's providing
access and services for all of those different applications.
If you're in an organization, really, of any size,
your email is so very important.
Email has to be able to go between email server
to email server.
How do those servers know where to send the email?
They ask the DNS server, of course.
Inside the DNS server is a special record
called the mail exchanger record, or the MX record.
This is how all of these devices know where to send your email.
So this is a very important record.
If you were to look at the mail exchange record,
it's very simple.
There's IN, MX, for the mail exchange,
and then the name of the mail server.
And that's it.
You don't have to define anything else.
Later on in the configuration file,
you will have an address record that
associates the name of that particular server
to a specific IP address.
So the MX record, relatively simple,
but very important if you want to be able to
receive your emails.
Another useful DNS record is the Pointer record.
You can think of this as the opposite of an address record.
An address record took a name and provided you
with an IP address.
A Pointer record means that you can provide an IP address
and come up with a name.
And offhand, this doesn't seem like something
that you would use a lot.
There are certain applications that
use this capability to be able to transfer information
between services.
You can see this information in a reverse map zone
file that I have here.
And really, it's this part down at the bottom,
where you're adding in an IP address
for a particular subnet.
Here's our IN for internet, the PTR
designation for the Pointer record,
and then you're simply assigning names
where you happen to have an IP address
for that particular subnet.
Hopefully, that's given you an idea
of what you can expect if you look
at the configuration of a DNS server.
Should be able to now recognize some
of the most popular records, and be
able to understand what those records are doing inside
of that server.