Wii / Wii U / Switch:
[UDP Ports]
~All Games~
1-65535
OR
1024-65535
~Mario Kart Wii Only~
22XXX (where XXX is the last 3 digits of your console's serial number)
[TCP Ports]
Wii U / Switch:
6667
12400
Wii / Wii U / Switch:
28910
29900-29901
29920
You can also check for the fastest DNS server using namebench.
And you can optimize your router's MTU by reading this guide.
[UDP Ports]
~All Games~
1-65535
OR
1024-65535
~Mario Kart Wii Only~
22XXX (where XXX is the last 3 digits of your console's serial number)
[TCP Ports]
Wii U / Switch:
6667
12400
Wii / Wii U / Switch:
28910
29900-29901
29920
You can also check for the fastest DNS server using namebench.
And you can optimize your router's MTU by reading this guide.