Introduction to DNS (Domain Name Services)

hello again as you know I am Eli the computer guy in today's class is introduction to DNS so we are going to go over the basic concepts for domain name services today so that you understand how they work in the networking environment now this is the introduction to DNS class so we today we're going to be talking about DNS within a normal Network environment we are not going to get into some of the more complicated internet DNS stuff so we're not going to be talking about MX records or C names or any of that we're just going to be talking about DNS so that you guys have a basic concept of DNS for when you're doing networking now what is DNS DNS is the server service that map's domain names to IP addresses now as I've talked about before remember many of the things that we humans find easy computers find completely useless so for computers when computers are trying to gain access to something on the net local network or the internet they do that by using an IP address now we as humans it's very hard for us to remember IP addresses you know 192.168.1.5 208 dot 50 5.66 dot 4 that's very difficult for us to remember so we use domain names computer names host names such as server or cnn.com well the thing is your computer can't use cnn.com if you go to your web browser and you type in cnn.com that doesn't do a whole lot for the computer that is not what the computer needs in order for you to go to the website cnn.com what the computer needs is the IP address for the server that houses cnn.com once it has the IP address then it can route your browser to that IP address then it can grab the website and then it can display it for you the same thing goes with if you're trying to connect to a file share if you were trying to connect to the shared drive on a computer named server server doesn't mean much to the computer the computer needs to know the IP address once it knows the IP address then it will send you to that IP address which has a folder named share and then you can access it this share files well DNS domain name services is what map's those domain names to the IP addresses so if we did not have DNS in the world we would have to remember all those horrible IP addresses and would make life basically impossible so when we're talking about DNS this is what we're talking about again when I when I talk to you guys since you guys are new many of you guys are new in technology especially if you're taking an introduction to DNS class one of the biggest problems for new people is that they think services do more than they do and so they then get confused it's very important understand that DNS is only one of the services that you use on a modern tcp/ip network and all it does is map domain names to IP addresses so DHCP the dynamic host control protocol that is what dynamically assigns IP addresses to computers when they connect to the network that is a completely different service than DNS and that can be housed on different servers now many times DNS and DHCP are housed on the exact same server so again a lot of people get confused and they think that they are the same service when in reality they are completely different services now when you're going to be working with DNS frankly most of you guys most of you guys when you were working with DNS and a network environment are probably going to be dealing with your your standard small office home office router so DNS and DHCP and a whole bunch of other things are you usually built-in to these small small business routers so most of you guys when you're dealing with DNS this is what you will be dealing with now these things there's generally not a lot you can do with it basically you can turn dns on you might be able to map a couple of domain names but but that's about it they're very simple obviously you spend a hundred bucks on one of them you turn it on you plug it in you're done DNS either works or it doesn't you throw this away and you buy another one once you get into the enterprise environment you will generally be dealing with a one of two different types of DNS servers you will either be dealing with Microsoft DNS so I'm currently doing a track of Windows Server 2012 where we're going to be doing a class on DNS setting that up in Microsoft server world so if you're in the enterprise world you will most likely either be dealing with Microsoft DNS servers or you will be dealing with Unix Linux bind servers so if you want to learn more about DNS you want to learn about the really hyper hyper complicated stuff take a look for by b.i n D so with those if you're using Microsoft DNS or you're using bind you can do really really really really complicated things but for most of you guys with DNS it's it's pretty simple stuff all that it's going to be doing is it's going to be mapping the domain names to the IP addresses now one of the important things one of the reasons that I brought up that DHCP is different than DNS is because many people get confused about this they put DNS on one server they put DHCP on another server and then their network doesn't seem to be working right well the important thing to remember is remember DHCP dynamically gives IP addresses DNS houses the the the domain name to IP address it Maps that right well in order for a modern network to work properly you need to have something called dynamic DNS setup so when you're dealing with one of these small business small business routers you're dealing with a network that's set up properly when the DHCP server gives an IP address to a client computer it's actually doing two things one it's giving the IP address to the client computer two it's telling the DNS server what the IP address of that client computer is so dynamic DNS is DHCP dynamically writing to the DNS tables to say to map those host names or those domain names to IP addresses so if you have a DHCP server off in its own little world and it's not talking to the knee and s server the DHCP server will continuously give out IP addresses but that information will not be recorded on the DNS server so if you try to ping let's say PC 2 or computer to write and dynamic DNS hasn't been set up that won't be able to work because within the DNS server that information has not been written so this is just something that you should keep in mind this is one of the big problems people get into especially when they try to get into Microsoft enterprise networking type stuff is that they don't have this dynamic DNS configure properly and so they're giving out IP addresses but the host names are not getting mapped to the IP addresses within DNS and then when computers try to talk to each other or communicate with each other it all turns into a big mess so the first thing that you need to remember with DNS is this dynamic DNS it dynamically writes the host names and IP address into the DNS tables the other thing that you may not think about but but you will hear about more when you go into the more complicated stuff with DNS is one of the things it's called reverse DNS so DNS the primary thing that DNS does is DNS maps that hostname to the IP address now as we've talked about in the hacking class what's really cool is if you can set up a server or you can set up a system in the middle of a network to start redirecting computers to a different server so so I did a class where you you hacked your hosts file and in that you can actually have google.com go to a malicious server go to a server that is not actually Google servers it's your own server and then you can download viruses or whatever so that is done because you're able to get in and redirect that computer to a fake IP address well one of the reasons that can happen is because in the normal DNS scheme you map the domain name to the IP address but you don't verify that the IP address is the IP address that it should be so what you can have especially in Microsoft world and in bind world you can have something called reverse DNS so DNS map's the hostname to the IP address in reverse DNS it maps the IP address to the domain name so if your computer is supposed to go to let's say server in an enterprise environment when you're gone about to go to server it will it will go to the DNS and we'll make sure that server is supposed to go to 192.168.1.1 but then it will also do a query and it will say what is 192.168.1.1 supposed to be and if you have reversed that DNS setup it will say 192.168.1.2 is supposed to be server that way you make sure that the hostname maps to the IP address and IP address maps to the hosting and then you get more security so these are some of the basic concepts that you should know with DNS I want to show you a couple things just to just to make sure you guys understand what's going on we're going to go to the whiteboard so I can explain this a little more let me transition so basically as I say when you have your little computer so your computer is here and it is obviously connected to your switch now when your computer wants to go to a website such as C and calm again your computer doesn't understand what cnn.com is that makes absolutely no sense to it so what it's going to do is it's going to go out and within your computer a DNS server will have been configured so it might say that 192.168.1.1 is the DNS server that's been configured for this computer so it will go to that IP address 192.168.1.1 and it will say hey I want to go to cnn.com this DNS server will then return and it will say well cnn.com is 208 dot 5566 dot for your computer will then take this IP address and we'll go out to the router it will go out to the internet and then it will look for 208 dot 50 5.66 dot 4 and that will take it to cnn.com and then cnn.com will return the web page so this is basically how DNS is going to work for you now it gets a little bit more complicated this when we're going out to the internet so when we're going out to the internet again with the DNS server the important thing to remember about the DNS server is a DNS server is generally if it if it's the local the land DNS server it's only going to have records for the local area network so your DNS server that is sitting in your building only has the records for the computers that are in your building it does not have the records for all of the computers all the websites out on the internet so it's really going to be happening is when you want to go to cnn.com you're going to go through the switch that will go to your local DNS server that's connected to the router which is connected to the internet in your local DNS server your DNS server will also have DNS server information so it will have its own records but then if it can't find the the the host named IP address mapping in its records it will also have DNS that it should look for if it can't find the information its own records so it'll have its own records but then it'll also say let's say 209 77221 is its primary DNS server and to 10.67 22.2 is its secondary DNS server so if you're trying to go to cnn.com it's gonna go through the Swick it's going to go to the DNS server your DNS server is going to look for cnn.com within its own records well when it looks it's not going to find that information so then it's going to see what its primary DNS server is and it's going to go out to the internet or wherever that DNS server is located and then ask that DNS server what the IP address of cnn.com should be if the outside DNS server has the information it will return the IP address to the DNS server which will then return it to your computer which will be like 208 77223 and then now you will be able to go out to cnn.com using that IP address so this is something that's very important understand is on your local area network not only does your DNS server have tables that have the host name to IP address is there but it will also have its own DNS servers that it will go query if there is no information within its table so this is what happens now when you're on the local network and you have your computer and it's connected to the switch and then you have the DNS server here basically if you ask for something like I need to go to computer named server that will go up to the DNS server you'll say I need the information for server DNS will go oh server equals 192 dot 168 1.2 it will return that IP address your computer will then go to 192.168.1.2 through the local switch and then be want to connect to any of the shared resources there so this is basically how the DNS works in the real world this is not overly complicated stuff but it is what you should understand so the DNS servers map the hostname or fully qualified domain name to IP addresses remember that the DNS tables you want them to be dynamic you want them to update whenever DHCP gives out an IP address because if it does not dynamically update that means you have to go in and manually edit the DNS tables all the time basically reverse DNS is something you get into basically once you get into the more complicated stuff with that maps IP addresses - domain names why this is done is for security to make sure that you're not getting redirected off to someplace that you shouldn't be now the big thing again with these DNS servers is not only not only do they have their own tables full of information within them but you also program DNS servers for DNS servers so within your router this will have its own DNS configuration but then if it cannot find of the domain name to IP address within its own tables it will then look to the DNS servers that have been configured for it to see if they have the proper information again we talk about things like security and hacking one of the big issues here is if you can get into the tables for one of these DNS servers and you can modify the tables well then you can redirect computers willy-nilly however you wish and start causing a lot of problems so if you have a DNS server on your local area network and somebody nefariously is able to get in and rewrite some of those tables so that so google.com no longer goes to Google servers but it's redirected to some other persons the important thing to realize is that there's really no additional security basically the computers will all get rerouted because all that happens within this DNS process is your computer says I want to go to CNN or I want to go to google.com then the router the DNS server returns well google.com is 208 60 6.50 5.4 well somebody can go in and instead of sending it to that IP address it sends it to to 220 77 8.2 there's not a lot of security in there but that gets into some hacking and some security and some other stuff but but we're not going to get into that now I just wanted to give you an overall introduction to DNS to you that you guys understand what's going on again we're going to have more classes we're going to have a class on actually setting up DNS server in the windows world we're going to have a class on internet DNS so again mapping all this information when you're dealing with the internet you have things called MX records c cname records a records things like that but that will be in a different class I just wanted to give you an overview here so that I can take those additional classes so as you know I'm Eli the computer guy this was introduction to DNS as always I enjoy teaching this class and look forward to see on the next one

Channel: Eli the Computer Guy

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Length: 19min 18sec (1158 seconds)

Published: Wed Mar 13 2013