in this video we only look at a number of concepts that help to explain how part of the internet works and more specifically how the world wide web works we'll be describing what the euro L universe was all slow caterers explain the term fully qualified domain name domain name and IP address we're going to describe how to main names are organized we're going to understand the purpose and function of the domain name service and its reliance on domain name servers and we're gonna explain the service that's provided by internet registers and why they're needed so let's get started so you'll be quite used to this this is a browser and as you're well aware you can type a web address up here in the browser press ENTER and then hopefully fingers crossed a web page appears down here now you may have used different words for this in the past you may call this a web address a URL um it's actually split into number important parts and they have different names so this part here is what's known as the website domain name so I think it's like BBC Dakota at UK amazon.com or Craig and Dave dot org when we add the hosts onto the beginning so in this case that's the www which is the most common type you typically see this entire section now becomes known as the fully qualified domain name once you add the access method onto the start which is typically HTTP or HTTPS for a secure encrypted website and we'll be looking at various protocols in another video then we have the location here so we now know the method to access it the host and the domain now we've got to the site we have the location within that site so once we've gone to the site is I'll see a number of different web pages and we're going to access a resource in this locations we've got like a folder structure here and then finally the name of the actual file so in this case this web address is actually getting a PDF into your web browser the entire thing all the way from the method to the resource that's what's known as the URL some candidates confuse this bit say all type in here the Yoel Craig and David org well that's not the URL that's the website domain name that's the fully qualified domain name it's the entire string including all of these elements which is technically known as the Uniform Resource locator or you are L so talking about domain names for a second who are they run by you know who decides what domain name there's one company out there that has the domain name BBC Cody at UK there's one that has google.com and Google Cody at UK once that the main names gone no other person can use it so clearly these can't be run by any single government because the Internet's a worldwide thing well they're run by companies called Internet registers now these are five global organizations governed overarching lis by the Internet Corporation for Assigned Names and numbers I can and these large companies these global organizations hold a worldwide database of all the domain names and who they belong to so effectively if you buy a bit of web space through a local ISP they will have a number of domains they can assign you but at the very top level it's these global organizations which are controlling these worldwide databases of domain names they're the ones that make responder make sure that no domain name can be used twice and every domain name therefore is unique which is an essential concept of the world wide web so I'm talking about domain names for a second it's important to exam to understand how they're organized so domain names are struck into hierarchy as you can see here now we've just shown part of the hierarchy the small domains appear lower down and the higher up the more generic and global the domains when you write a domain out you write it out from the bottom up using dots so here's a good example BBC Cody UK that is BBC dot code dot uk' so we can see here we have what's called a third level domains that's one of these small ones down here now if we move up the hierarchy we have a second-level domain as we go to the top we have a lot called country level domains now you'll be quite familiar with these top-level ones a lot of sites have docked code or UK at the end in France a hub far for France there's also non specific top-level domains like generic ones like condor org and.net so let's have a look at the relationship between domain names domain name servers and IP addresses now for this we need to get our head around a few terms we already know what the fully qualified domain name is that's a domain name which includes the host like www.craigslist.org inhalation you spoke about earlier it's an internationally agreed structure which classifies the area and Internet resources where it resides and that structures into a hierarchy which we just saw and finally IP so if you don't know already an IP can be thought of as a unique address which is given to a single network device so it performs a similar function to your home address every single device which is coached the Internet has to have an IP address now these IP addresses can change which is something we're going to talk about more in another video but for now just be happy with the fact that every device on the Internet must have an IP address it would be hard for you to post a letter to someone if their house didn't have an address and the same thing is true here now IP addresses are typically strings of number a traditional version for IP address could look something like this it's a set of four numbers there's also something called IP version 6 addresses which are much more complicated and again we'll get into those in another video but effectively every website out there has an IP address now as you can imagine these aren't very handy if I said to you oh yes the BBC's web address it's 1/9 3.60 3 dot 99.1 73 that's not as easy to remember as BBC dog code at UK but every website out there has to have an IP address so let's have a look at how the whole domain name system works with these IP addresses to make things easier so we're going to step through an example so here a user has typed into a a web browser a URL request for Craig and Dave dot org the browser extracts the fully qualified domain name because they were typed in the whole URL it extracts the fully qualified domain name it then sends this off to the local DNS server there's probably been run by your ISP now here's the key bit the local DNS server has a lookup table and the lookup table Maps the web address you've asked for with IPS so look down its list for Craig and awwa and David org if it finds it it will return the correct IP to the browser now there is a chance that this DNS doesn't have this mapping entry in its lookup table and that's quite possible if this is the case it passes the request upwards on to a much larger regional DNS now these have much much bigger lookup tables so the chances are is it will find the matching entry in a likely event the regional domain name server doesn't have an entry it passes it all the way up to what called network service providers now there's much much fewer of these on the Internet and these are absolutely massive tables of web addresses and matching IPs either way once the web address is found the IP will be passed back to the browser incidentally now that passes back it will place the entry into these tables which means in future getting the lookup will be much quicker once the IP address is back here we can now send a specific get request to the web server that actually holds the Craig and Dave website because it's the IP we need to know yeah we've typed in Craig and Dave to org that's told us where it really sits that's the IP address now I've got it I can use the IP address and jump over and then obviously the files return to the browser so essentially there there's the really important link between IP address and your fully qualified domain name which is inside your URL and the role that the DNS the domain name system plays in matching those two up