DNS is for the Internet, what oxygen is for life. Though we constantly use it, we are unaware of its presence. DNS has come a long way since Stanford Research Institute’s Network Information Center (SRI-NIC) maintained a file called hosts.txt which contained host-names and their corresponding IP addresses, to a complex network of databases called name-servers.
DNS was originally designed to make it easier for us to memorize names (host-names) rather than numbers (IP addresses). Gradually, many applications and protocols used the host-names and IP addresses as a basis to authenticate the host. Thus DNS security came into being, since wrong information from a DNS server, can disallow a legitimate request from a legitimate client.