All right, so 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,
D H C P Dynamic Host configuration protocol. And then the last is I Pam, which is I p 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 what DNS does for us
because you and I are good with names, but we're not good with I P 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 dot com. I have no clue with the I P addresses,
but we have to remember when hosts are making a network connection. One of the things they need is an I. P address.
That's a Layer three resolution that has to happen.
So it's DNS that we go to.
Our clients are configured to know who their local DNS server is.
So 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 I P address.
The client is then able to add that layer in the Layer three pocket 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 I p address changes. As new hosts come on to the network,
they are also able to register with DNS. So DNS is a lot easier to manage than it was years ago.
As a matter of fact, many years ago, I 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
and as DNs evolved, allowing host register dynamically, which is much, much easier than it used to be.
But it's really critical service and everything is based on the database, and 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 curies, specific records are used,
the one we think of most often when thinking of Deanna's is an a record
also known as host record.
This is the record that takes a known F. Q D N and resolves an I P address.
We connect to amazon dot com, and we get an I. P 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,
so 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 I P. V 62 f Q D n resolution,
The PTR record when a record is actually the opposite of a host record.
What is going to do is if you have an IP address, it will find the fully qualified domain name.
when am I going to find the I P 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 point of resolutions or reverse resolutions.
As a matter of fact, they called the zone reverse lookups zone, whereas when you're using a host record, that's a forward look up.
There's a handful of others
start of authority, So a is the name server that's authoritative for the zone.
Your PSA is usually the first DNS server that has name resolution For that zone.
You may have another other name service Redundancy. That's what the NS records are for.
The SRV or service records are really important because they list the critical network services and 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 L. D. A P server. Here's the I P address for it
for a Cabrera's key distribution Asian server or a global catalog server or mail server.
So the service records have all the services in which servers are running them.
There's also a record type called the CNN name 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 I t. Would want to have our servers named after Star Trek characters rather than W W W. How boring is that?
But we know that our Web browsers are going to connect to a server. Www.
So we create an alias record that says when they type out, www, send them to serve your pi card or whoever your favorite character is.
I don't want to go down the narrow 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 Baltimore server onto the network.
That doesn't bode well.
And finally, the last record type is the mail server, an MX record that will indicate where the mail servers are.
So these records are really the heart and soul of DNS,
and these are the records that are used any time you make a query to the DNS server.
The way DNS works is let's say that I'm trying to get to google dot com or something that basic
or the Web server for google dot com,
even though we don't type out Www anymore. That's understood within the Web browser
I as a client. Type out www dot google dot com and I send DNS query to my local DNS server.
It's called the DNS resolver.
Now, because the google dot 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.
So the first thing my local DNS server does is it goes out to the Internet and contacts of root server,
and there are multiple root servers out on the Internet,
and this is like the ultimate point of origin for DNS.
So the DNS resolver says, Hey, route. Do you happen to know where w W w dot google dot com is?
And the root says Nope, but I do know where the dot com server is.
So my local DNS server then goes to the top level domain name server dot com in this case and says, Hey, do you know where at www dot google dot com is
the com server comes back and says, Nope, but I do know where the Google name server is
my DNS server. Benson security to Google and says, Do you know where www dot google dot com is?
Google says, Yes, I do.
And here's the I P address for our Web server
that's passed back to my local DNS server. Who is the resolve? Er, who then passes it back to me is the client, and now I'm able to connect to Google's Web server by AIP.
Now there are other ways to expedite this. There's cash, and there's some other things you can figure but in and of itself. This is kind of the hierarchy that DNS uses to provide name resolution
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,
and so DNs is really important.
It's a hierarchical database, starting out at the root with the top levels and then secondary levels.