The addresses of Internet protocol (IP) are avital resource for the Internet. In the network, IP address is assigned to every interface which connects to the Internet. The addresses are still assigned by using Internet Protocol version 4 (IPv4). IPv4 has demonstrated robust, compatibility with vast range of protocols, applications and easy implementation. IPv4 had been supposed to cover all the network interfaces, however with huge increase of the number of devices (computer, mobile, tablet, routers, server, etc) the reserve of assigned addresses is exhausted. IPv6 has been deployed for providing new services and for supporting the internet growth. This study compares the key specifications of IPv4 and IPv6, contrasts IPv4 and IPv6 header?s fields, the structure of headers, explains advantages of IPv6 and disadvantages of IPv4, and why.