With the emergence of mobile devices and the rapid growth in mobile networks, file sharing became a common activity. However, in order to share files between mobile devices, users need to use different software systems depending on situations, which makes it tedious and inconvenient. In this paper, we propose FFS, a fast file sharing approach for peer-to-peer file sharing. FFS overcomes network limitations with an approach that dynamically selects a suitable one among various NAT traversal techniques.