The Internet of Things (IoT), with its ability to collect data using sensors and store the useful data over the cloud, has become the existing standard in building up smart homes and smart cities and for other smart applications. To build such smart applications, the routing protocol used in the network layer of IoT should be capable of effectively forward and route the data without consuming much power, memory, bandwidth processing capacity, as the IoT devices are resource constrained. The favorite routing protocol for IoT is Routing Protocol for Low power and lossy networks (RPL), which uses several metrics to determine the path cost. This paper provides an analysis of performance of such RPL based IoT network. QoS parameters such as Throughput, Packet delivery ratio, Network convergence time, Latency are computed and analyzed. The IoT network simulated with varying number of nodes are compared for the aforementioned QoS parameters. The simulated results show that the performance of the network improves when the network size increases, at the cost of increased delay. © 2018 IEEE.