Dual-band routers transmit on not one but two frequencies, i.e. the standard 2.4 GHz band and the less crowded 5 GHz band. If you connect a Wii to your dual-band router, be careful to add the MAC address of your Wii to the correct MAC filter.

With dual-band routers, you can place MAC filters on both frequencies. Because a Wii only communicates via the 2.4GHz frequency, you only need to add the MAC address to the filter for this frequency (if you have enabled MAC filtering).