With the advances in wireless communication technology, mobile applications are gradually being introduced as part of our life. IEEE 802.11 is one of the most popular wireless communication technologies. Prior studies toward layer-2 and layer-3 handoffs assume that Extend Service Set (ESS) exactly matches a dedicated subnet. However, an inter-ESS with intra-subnet handoff and an intra-ESS with inter-subnet handoff may also be possible. Such mismatching ESS-subnet configurations result in performance degradation. This paper proposes FCS, a Further Check Scheme which detects the change of subnet after an intra-ESS handoff and eliminates unnecessary handoff latency after an inter-ESS handoff. The experimental results show that FCS outperforms the conventional implementation of NetworkManager under Linux in terms of handoff latency.