 I have my Linux machine, my client inside Virtuobox and let's have a look at doing some DNS client operations and we'll use NSLookup to basically see the mappings from domain names to IP addresses in the internet. Normally this happens in the background but we can have a command line tool to inspect things ourselves. Currently it's not installed so I need to install the DNS utilities. DNS Utils is the package which includes the things that I want to use in particular NSLookup. It may be installed on your system, in mine it's not. So it's going to install some additional packages and use about 12 meg of disk space so that's why it's not installed by the cut-down server initially. Yes, I'll install and now I should have, and just to show by installing DNS Utils I should have the command I'm looking for which is NSLookup. NSLookup does a manual lookup if we provide a domain name. For example, google.com.au, it does a lookup and tries to find the corresponding IP address and it finds the answer is 216.58.199.67. The purpose here isn't to explain how the domain name system works, it's to show what NSLookup does for us. Normally DNS runs in the background, we don't do this. For example, when I open my browser and type in a domain name, like google's domain name, then it calls a DNS client to do the lookup for us. We're basically manually calling the DNS client to do the lookup using the program NSLookup. So it gives us a mapping from a name to an IP address. You may see different information because DNS, DNS is a complex system where we may have multiple mappings, we have cases and that may mean that people in different locations or on different computers can get different responses. Just looking at the output of NSLookup, the first two lines are not telling us the result but telling us the server that we got the answer from. So basically we asked this particular server, 1387176.10 and that may be given as a domain name there in some cases and here would be the IP address and port 53 which is the port number used by DNS servers. We asked this server, what is the IP address for this domain name? And the answer we got back was this 216 address and it's a non-authoritative answer, meaning the answer we got back is like a cached value. It's not coming from the authority server where this domain name is registered. So it may be different in different cases and it may be out of date because it's a cached value but normally it would be a correct. Try it on different domains. Type sandylands.info and it tells us the IP address for that is 103.363.107. We can, and it tells us that we got it from the same DNS server and that DNS server would be my local DNS server for the university network. Try a couple of others and let's look up on Facebook, some different output here. Again, we've done a look up, we've got an answer but we see that there's that Facebook or www.facebook.com is really an alias or a nickname. The real name or canonical name is star.mini ctanr.facebook.com and the IP address given is for that domain name. So this is saying that Facebook is just a nickname for this longer domain name. And again, the complexities of DNS means you may get different results depending on which regions you're in, which DNS servers you ask. A couple of others, google.com.au gives it, sorry, if we do and compare google.com this 216 address 199.68 and do google.com.au.67 almost the same 67.68, most likely they are both hosting Australian web server content although it's more complex than just going by the IP address. And we can, as another option, I'll just clear, we can specify which DNS server to look up. So when we just, sorry, when we type just the domain name then we'll ask our default DNS server but we can supply as another parameter a known DNS server. And I know that there is a DNS server with the address 8.8.8, which is actually the free DNS server that Google provides. So in this case, I haven't asked my default DNS server, I've asked a specific DNS server, there's all eights address and I've got the answer from that server and noting it's a different answer. So different DNS servers have different mappings from the same domain to IP address. And you need to look at the background of DNS and how, say, websites have content in different locations and to understand how all that works. So use NSLookup to do manual lookups with domain names and optionally supply a DNS server that you wanna ask to get the answer from.