Ever since I got my 3DS XL back in July of 2013 I have had nothing but issues with the internet features of certain games. Mario Kart always errors when searching for players, I am unable to visit most people in Animal Crossing New Leaf, and most can't visit me either. The weird thing is though that other games such as Pokemon X and Alpha Sapphire work perfectly fine online including both trading, battling and features like the GTS.
Over time I have had two different internet companies the first went out of business (both were broadband though). I've also had three different routers Belkin (had the old insecure sercurity), D-Link (quit working after a year or so), and Linksys (my current one). Even with all these changes I've still always run into the same errors and problems.
I have tried many things to correct these issues such as following Nintendo's error code suggestions like changing the DNS to the public Google one, setting up an IP Address for my 3DS and even setting it into the DMZ on my router's settings. None of which have worked in the past until now (but only sort of).
I recently bought a Wii U just after Christmas and have had the similar issues with trying to play Mario Kart 8 online, but after changing the DNS to a different public one (not the one suggested by Nintendo) it worked great online, and still has several days later. (Just as an extra note: I have played my old original Wii including Mario Kart Wii online before those features were shut down and it worked just fine It's only been the Wii U and mainly 3DS that I have had issues with.)
With sucess on my Wii U I figured I'd try out that same DNS on my 3DS, and it worked for a day, but then it went right back to the same old errors. Then I tried the suggested Google DNS by Nintendo again, it too worked for a day then errored again. Yesterday I put the other DNS back in, and placed my 3DS in my router's DMZ as I had not yet done this with my latest router, it too worked great yesterday, and today errors again. I simply don't know what to do. I really enjoy playing Mario Kart 7 and Animal Crossing online, but with these issues I have lost interest in both as it's such a hassel.
I also know it's not an issues with my 3DS as I have had it connected to two different internet sources elsewhere and said issues never arose once until I was back at home on my own Wifi. Is there any real fix to this? At the very least I wish I knew what the problem was. Thanks.