Subtitles of the Movie

The DNS name space is an important part of DNS, as it gives an understanding of why domain names look the way they do, and how DNS works. The namespace refers to the hierarchical layout of DNS names; the DNS namespace is laid out in an inverted tree. This means the root of the tree is at the top, and the branches of the tree grow downwards; of course this is all figuratively speaking. At the top of the DNS namespace is the root; all domain names start at the root which is defined by a null character. Note that domain names read from right to left, that is the highest level of the name space, the root, is the furthest right portion of the DNS name. The root is not normally explicitly specified in user applications, as most applications assume it. It is often explicitly specified in DNS server configuration files and is denoted by a trailing period. Below the root in the DNS namespace, are the top level domains or TLDs. These are the highest names in the name space, for example, .com or .net. These TLDS are maintained by the Internet corporation for assigned names and numbers, or ICAN, for Internet use. On the Internet, you must use one of the ICAN approve TLDs, if you're using the standard root servers. On a private network though, you can use any TLDs you want. You may see some examples in this course where I use the .tld domain as a TLD. This is not a legal Internet TLD and I do this just for the sake of example. It is bad practice to use illegal TLDs, even on a private network, in case you ever need to connect that network to the Internet. If you did you'd need to change all your illegal domain names. The remainder of the namespace is open for use more or less; there are few names that you can’t use but for the most part of it's wide open. You can register domain names beneath several of the TLDs including .com, .net, .org, .biz and .nam for example. There are also restricted TLDs such as .gov and .mil which can only be used by the US government, and .edu which can only be used educational institutions. You also have the option of country TLDs, based on your country codes, such as .us for the USA and .ca for Canada. Once you have a domain under a TLD, you can create as many sub-domains as you like, as long as they don't reach more than hundred and twenty seven layers below the root. For example, if you register the domain vtc.com, you can use sub-domains such as east.vtc.com and west.vtc.com without needing the register them. I cover the configurations of sub-domains later on in the course. Here you can see an example of the DNS namespace, with the root at the top; under the root are the TLDs, next come the regular domains, below those are hosts or sub-domains.