What Is DNS - Domain Name Server
This course goes through DNS or Domain Name System. This video provides an introduction to DNS, however the videos in this course are dynamic in nature. As DNS changes, videos are added or removed as required to make sure that you always have the most up to date information.
What Is DNS
DNS is a system that primarily maps a name to an IP Address. Although it can be used to do the reverse, it is primarily given a name and asked what the IP Address is for that name. This is the same principle that is used for a phone book. Given a name, a person is able to look up the phone number for that person using the phone book.
Hosts File
Before DNS, a hosts file was created on the local computer that contained a list of computer names and their IP Addresses. The problem with this approach is that all computers needed to have a copy of the same hosts file. With a few computers this was not too difficult, however as networks got bigger so did the hosts file, making it harder to keep up to date due to the size of the hosts file and the number of computers that the hosts file had to be copied to.
Nowadays, DNS is the preferred way to look up computers on the internet, however the hosts file is still present on modern computers. Whenever possible you should use DNS rather than the hosts file however in some rare situations it may be necessary to use the hosts file.
DNS (Domain Name System)
DNS was first developed in 1983 to address the shortfalls of the hosts file. It is a distributed database based on a hierarchy design. This hierarchy design means that it is possible to have two computers on the internet with the same name. For example ns1.example.com and ns2.example.com. The computers have the same hostname as ns1, however after this it is different. The full DNS address like ns1.example.com is referred to as the fully qualified domain name. Since the fully qualified domain name is different, it allows two computers to exist on the same network that have the same host name.
DNS Namespace
DNS Namespace can be divided up in to different parts. Each part can be stored on different DNS servers, which makes DNS a distributed system. This allows control of DNS to be divided up and distributed across the world. A DNS server does not need to hold all the data for a fully qualified domain. For example a DNS server may only hold data for the .com, .edu, .au etc part of the domain space. Other DNS servers may hold additional parts of the fully qualified Domain Name, for example Microsoft, Google, and Amazon. By these DNS servers working together, a fully qualified domain name can be resolved. This will be covered in more detail in later videos as well as other features of DNS.