NSlookup is a standard Command that you could see on the Network+ exam, and it's also one that you need to know about, be aware of, because it's very handy and we use this to test our DNS records. This will tell us what DNS is resolving and so what I want to do is show you a couple of ways to use this. Now NSlookup is a little different from a lot of the Commands that we can use at the Command Prompt, but with NSlookup, there are two modes. Number one, there's like a non interactive mode, and then we can put it into interactive mode. And so first, I'm going to run a non interactive Nslookup query. So if I just type NSlookup and I type Yahoo.com. And if I press Enter, it is going to go run the DNS search on Yahoo.com, and report back to me some information. Now notice what it's telling me, that it found, that under Yahoo.com, there are these IP addresses out there listed for Yahoo.com. Now if I chase one of those down for example, NSlookup 72 dash 30 dash 2 dash 43, and press Enter, it's going to come back, and notice it's showing me now the fully qualified domain name that it's finding for Yahoo.com, and I could run that on every one of these, and probably see something a little different on this fully qualified domain name here, or the full domain name. Now that's in non interactive mode. So I'm going to clear the screen, and now, I'm just going to run NSlookup and press Enter, and you're going to notice that this time, it has given me this default read back on my own machine here, but now the cursor, notice is this greater than sign. Well what I can do at this point, is start to do some different things with NSlookup. And if I just put a question mark, and press Enter, it shows me some help file information. And I'll show you just a real simple example of some things that you can do with NSlookup. The first thing is, for example, under this Set Option, let's say, Set Type Equal OK? If I say Set Type Equal MX. Now MX records should report back to me, the IP address for any records that handle mail exchanging, and this should basically be the IP addresses for their mail servers, and so I type Set Type Equal MX, press Enter, and then I will put in once again, Yahoo.com, and press Enter. It will take it just a second here, and boom there they are. I didn't actually hear a boom, but notice it's showing me that the non authoritative answer, if you know what that is, in DNS good, if you don't, don't worry about it. Notice here's the exchanger, and then here are the IP address for the mail exchange servers. And so again, you can start to see a lot of information. Now I want you to notice one thing here, we're getting a lot of information, a lot of IP addresses, and as a result, if you really know how to use these Tools, you can find out a lot of information, without even leaving your desk. And also just a little hint here, you can also see how just basic standard TCP/IP Commands can be used by hackers to gain a lot of information as well. So this is not really hacking information, but this can really start to open doors, and help you to build a profile. This is called, a lot of times you'll hear it called, Ethical Hacking, but you're going to use this type of information, and these type of Tools to find out how your system is set up, and if you're having mail problems, this will show you where the mails being directed, and you may think that the g.mx.mail.yahoo.com server is at a different IP address, but this is the one that's actually being routed to. And so you need to go correct your DNS file somewhere. So anyway that's NSlookup, now when I'm through with interactive mode, I just simply type exit, and I'm right back where I started from. Now there's a lot of things going on up here in NSlookup, and I would strongly recommend for the real world, that you jump out on the Internet, or you just kind of play with these things, and set in some different Commands, and just run them, and see what all you can do with NSlookup. This is a good Tool to learn and know, and you may see this one on the Network+ exam. So get a little hands on with it, just understand basically, that it is used to test to see what DNS is returning and you can use NSlookup to either ask for things, either as fully qualified domain names, and see what IP address DNS gives you, or you can put in the IP address and see what domain name DNS returns.
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