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Another DNS tool that you certainly need to be familiar with as you prepare for the 291 is the NSlookup utility. And this is a command line utility that performs queries or lookups on name server. So you might be able to deduct that from the name of the utility. So test the DNS name space and it can be used as a monitoring tool, not really can be included in the same section as the monitoring section in this chapter. There are 2 ways to use the NSlookup tool, in interactive mode and non-interactive mode. Now when you use it in non-interactive mode you simply open up the command prompt, type NSlookup, and then the query you'd like to perform and then press return, it gives you the results and then kicks you back out to the command environment. In interactive mode you're actually in the context of the utility the whole time so it's assumed you type NSlookup. To use it in interactive mode it's probably easier to show you by example. Open up the command prompt and just simply type nslookup. Now you're at a command prompt that takes you out to the default server. One thing about using the NSlookup utility is that you must have a correctly configured reverse lookup zone for error free operation. It's not that you can't use NSlookup without reverse a lookup zone but for error free operation you need to have that configured. And what I mean by this is this, when I type in nslookup, my DNS client will query, will say OK, where am I going to look for information? Well I'm going to look for my default DNS server. What do I know, what is my DNS client know about the default DNS server? It knows this information here. It knows the IP address. Well how does it resolve that IP address into a name beanserver.beanlake.org? It can do that because, in my reverse lookup zone, I have a record, a pointer record for 192.168.2.100. So if I didn't have that configured I would get an error message here, unable to resolve name. So now I'm in interactive mode and really it's not important to know the syntax here but you can perform lookups of things like, well, Bean SVR, by default it's going to look through the beanlake.org, because that is my primary DNS suffix. If I want to lookup information about a different computer, which exists, it's going to look in this in beanlake.org and it's going to timeout. So if I'm looking for a different domain, I have to specify the fully qualified domain name. The server beanserver.beanlake.org, which I am querying returns the address of 192.168.2.23. So this is mapped to this on this server. I can also change what servers I query with the context or with the syntax of the NSlookup utility. By the way how is that information known on that server? It's because this server is a secondary server. This server has a secondary zone information which maps that to an IP address. So that's how it's able to resolve that correctly. What else can you do, well to find out the other wonderful things that NSlookup is capable of make sure and be resourceful, type in the help option here and it gives you a list of syntax. There are lots of capabilities that NSlookup has. One easy thing you can do is that you can do a lookup on list, all of the records that are stored for a particular domain at the server. So to list all the records at beanlake.org here is all the records on beanserver.beanlake.org for this domain. So A records, NS records, delegation records and so on. This utility NSlookup you will use from time to time and actually quite a bit if you're doing lots of DNS administration but you need to know the purpose of the tool. Generally how to use the tool and know that you can use it in both interactive and non-interactive mode. To exit interactive mode remember the command exit and now I'm kicked back out to command prompt.