Computers and routers on the internet handle and transport data packets by the destination address, which is the IP address. The IP address is coded into every packet and routers throughout the internet inspect and deliver the packet to its destination using the destination IP address. That is a highly efficient way for computers and routers to work however it is not a good way for humans to work. Therefore the internet is designed using domain names which are human readable addresses for websites and remote destinations. Such as www.cnn.com or www.amazon.co.uk we can readily remember these addresses as opposed to 126.96.36.199 or 188.8.131.52
The Domain Name System is a register that acts as a lookup table so that a computer when it is given www.amazon.co.uk can go to its nearest DNS server and ask what is www.amazon.co.uk’s IP address? The DNS server will respond with the address 184.108.40.206
DNS is a vital service on the internet as all browsers immediately try to resolve domain names into IP addresses, if they are unable to reach a valid DNS server the request will fail even though the internet connection is physically sound. For that reason PC’s are configured with a secondary DNS server address to act as a backup should the primary DNS server connection fail.
Hostnames and IP addresses do not necessarily match on a one to one basis. Multiple hostnames may correspond to a single address as in the case of website hosting. Alternatively a major website may have one hostname but several IP addresses for load balancing or fault tolerance.
However being of such importance also makes DNS servers vulnerable to attack or rather to having their identity stolen. Many viruses fake being DNS servers in order to intercept DNS requests and return fraudulent replies redirecting unsuspecting users to alternative sites. A secure version of DNS was therefore proposed and the standards drawn up called DNSsec however after nearly 5 years it has gained little traction within the internet community at large and is rarely implemented.