Realization of congestion in software defined networks Software defined networking has brought a rapid change in networking industry by providing programmability and abstraction. it also enables centralization of control in infrastructure. In this paper, we describe the results of our experiment to determine the performance of SDN by simulating Open vSwitch under conditions of congestion. We did experiments on MININET by creating four compute nodes and observing their behaviour under congestion. The connections were made by using open vSwitch (OVS). We generated a lot of traffic between VMs using iperf and determined at what level of traffic Open vSwitch saturates leading to a drastic drop in throughput. We found that packet loss and throughput reduction can be observed when we increase number of parallel connection between nodes. Moreover the change is always sudden and drastic when it reaches the threshold value. Several experiments were performed to analyze the throughput variations caused due to traffic increase and the reason behind those variations.