In wireless networks, devices can be equipped with multiple interfaces to utilize multiple channels and increase the aggregated network throughput. Various channel assignment protocols have been developed to better utilize multiple channels and interfaces. However, the research of channel assignment protocols is still lack of a good simulation tool that can content with a variety of requirements and specifications of channel assignment protocols and conduct data collection and performance analysis. In this paper, we propose MIMC-SIM, a generic simulation framework for multi-interface and multichannel networks, built in INET/OMNET++. In MIMC-SIM, we put a new layer between the network layer and the MAC layer to provide a generic code structure and flexible extension for implementing channel assignment protocols. We also examine one of the channel assignment protocols within our simulation framework to study its performance.