[MUSIC] Hi, welcome back. In this lesson, I want to talk about some basic network ideas. First, where is a website? When we type in google.com or amazon.com, or any other website's name, where does it go to get the information? For example, if we type in yahoo.com we'll get Yahoo's website. Our computer finds that information by requesting that yahoo.com is looked up for us. And Yahoo is really identified by this long number. We read this as 209.191.88.254 and it's called an IP address. IP stands for Internet Protocol. Now normally, we do not need to know the IP addresses because they can be looked up for us. By using yahoo.com, we allow a service called a domain name service or DNS to find the IP address for us when we use the name. This way, we never have to know the IP address which would make it much harder to reach Yahoo or other websites if we actually had to know that number. This DNS runs on computers associated with our hosting service. It also runs on computers associated without ISP or smartphone provider. Now, ISP is who is you use to reach the Internet. This stands for Internet Service Provider. And if you're using your smartphone or some other smart device, it is probably your cellular provider that is also your ISP. So, this service DNS, let's us use name rather than a complicated numbers and syntax. And it also protects us from changes to the IP addresses. For example, the IP address above the 209.191.88.254 that belongs to a specific piece of equipment owned by Yahoo. Now, Yahoo can change equipment, add equipment, change IP addresses as they need to. But if we have to follow that, it would be very, very difficult for us to ever reach Yahoo as they made changes. Instead, if they make changes, the new correct changes are looked up whenever we use yahoo.com. So, let's give it a try. Go to this website and we'll see what we have here. We have the IP address that I mentioned and I'm going to click Search. Now this is a Whois Lookup and it should show me information associated with this IP address. Now, it's asking here for me to verify that I'm not a robot, meaning it wants to know that I'm a real person and not a program trying to abuse their site. So, we'll wait for a moment while it's looking up and notice here we see lots of information about this IP address. Now we're not going to read this through, but we can see it belongs to Yahoo. And we can also see that the location of the IP address, the physical location, is in Beijing, China. So, this means that when we're using Yahoo, we might actually be accessing the server that's in another country or if we're in China in our country. In this case all this information is hidden from us, so we don't have to remember it, follow it, write it down that sort of thing. Whenever we want to access Yahoo and this is true for any other website we want to access like Google or Amazon. All of them work based on IP addresses but humans would have trouble following the IP addresses and keeping track of all the details. So, DNS lets us use names to hide this complication.