Complete and accurate network topology is the basis for the network management. With the increasing diversity, transparency, dynamics of the link layer devices, discovering the link-layer network topology becomes increasing challenging. Existing works on link-layer topology discovery is based on the assumption that the network is static without mobile devices. However with popularity of wireless access, there are more and more mobile devices, making the network more and more dynamic. In this paper, we propose an algorithm for discovering the link-layer topology under dynamic networking environments. Simulation experiments on ns-3 and the real-world networking topology measurement results indicate that our algorithm could exclude the impact of mobile devices and discover the linker-layer topologies efficiently and accurately.