I think that may be the case but I still don't know...
It's a crappy Media-com router @_@
When it doesnt work i usually use my mobile AP
Toast Ninja
do you know what kind of router you have?
That may be causing issues.
I had a real cheap Belkin. At first I was able to connect to online matches, then suddenly (without any changes to my 3DS or my router/internet settings) I was unable to connect anymore.
I could still view the eShop and watch Netflix but no online multiplayer for any games.
After looking it up a lot of people with Belkin routers were having all kinds of issues with online connectivity with their 3DS systems.
I tried connecting to my neighbor's router. Which is a linksys.
I had no problem playing.... when the connection was in a decent range that is.