The idea of the Internet of Things is to connect every physical device with internet. Each device should be presented by a unique address of Internet Protocol. There are two versions of IP known by IPv4 and IPv6. IPv4 assumed to cover whole network interfaces. Since the appearance of IoT, number of connected devices increased sharply and IPv4 could not afford this enormous numbers. Therefore, the solution came by introduced IPv6 to afford this massive number in IoT environment. Despite IPv4 provided interoperability with several types of protocols, robust and easy implementation but it's vulnerable for several kinds of attacks. Therefore, IPv6 introduced while having security protocols such as IPsec, neighbour discovery protocol and Secure Neighbour Discovery Protocol. However, due to IPv4 still working as well as updated with security components, there is need to interact between both versions of protocol. Therefore, there is need for interacting mechanism between both them. These mechanisms made implantation of IPv6 complicated and consumed more resources. Besides, there are threats for attacks. Therefore, security features in IPv6 are not enough and there is need for a new defense line that can secure network services and IP from attacks. Intrusion Detection mechanism considered good mechanism to provide protection due to it works based on two levels Host and Network. Besides, it uses several security approaches such as signature-based and network-based. However, considering this tool as it's in IoT environment will not bring the light of security in IoT. Therefore, it should be developed while considering features of IoT devices to secure IoT environment. To achieve this, we have to investigate every feature, component and operation in network. This review paper aims to analyse difference between IPv4/IPv6 and point out security threats related to IP in both versions. Also, identifying main security threats to IPv6.