To support delay-sensitive applications on IP over wireless LAN (WLAN), both layer-2 handoff (L2H) and layer-3 handoff (L3H) must be conducted efficiently. Prior studies toward a fast L2H/L3H assume simple networking environments where Extended Service Set (ESS) exactly matches subnets. This paper identifies performance issues associated with inter-ESS L2Hs and L3Hs under mismatching ESS-subnet configurations, and analyzes actual performance impact on existing systems. Experimental results show that inter-ESS L2Hs are much time expensive than intra-ESS L2Hs while mismatching ESS-subnet settings lead to either time-consuming L3H detections or redundant L3H executions. We also discuss possible remedies for this problem.