IoT makes the smart cities worldwide possible. Smart home, smart farming, smart climate, smart wellness, smart government, and more are all kinds of smart towns. IoT is also used in the petroleum, gas mines and manufacturing sectors. IOT improves efficiency, optimizes prices, optimizes human capital, retains predictions and provides a lot of convenience to human life. Security issues are growing with involvement of large number of different devices and voluminous processing of data. Protection and privacy problems are the key reasons why IoT does not thrive. One of the main threats is vulnerability to DDOS attack. This paper presents use of block chain based methodologies to mitigate DDOS attack in internet of things. It provides a critical analysis of available block chain based architectures to encounter DDOS attacks.