Now a day’s people want comfort and automation in their day-to-day life with one click. For that IoT is the most emerging paradigm, and to become an indispensable part of IoT the wireless sensor nodes have to be integrated with internet. All IP-enabled nodes shall be communicated with any of the sensor node with the help of internet. So, with increasing use of internet trends some security issues like data privacy, authentication, access control, etc. have also become an essential part of this communication. This paper presents a brief study about Internet of Things (IoT) and their features, working and related security issues. Here, brief study mainly focuses on authentication related issues at gateway. It is one of the security related issues and very important aspect for maintaining confidentiality and Integrity of data coming from the sensor node