When my father had WiFi problems in his apartment, too many dead spots for a decent FaceTime conversation unless he stayed tethered near his Comcast Xfinity WiFi box, I picked up a Linksys Velop mesh WiFi router set for him while in the USA. It could not have worked out better. All the WiFi dead spots were gone, my father can FaceTime wherever he wanders. Velop truly ‘just worked’ out of the box.
Velop and similar ‘mesh’ WiFi routers from Google Nest, Amazon erro et all are good products but I do not recommend any of them for WiFi use in Japan: they all lack support for the IPv6 protocols used by NTT FLETS Japanese internet service providers (ISP) and the NTT NGN backbone.
Goodbye PPPoE (IPv4) Hello IPoE (IPv6)
The problem with Nest, error, Velop is the same one with the, now outdated, Apple AirPort Extreme (part 1, part 2): no support for DS-Lite and Map-E IPv6 protocols used by NTT FLETS. Both DS-Lite and Map-E use IPv6 IPoE (IP over Ethernet) and replace the IPv4 only PPPoE connection protocol.
IPoE is also called IPv4 over IPv6 which means all IPv4 packets are encapsulated inside IPv6. Fast internet connections in Japan use IPv6 but this means that your home router needs to encapsulate everything IPv4 in IPv6 before going out on the NTT internet backbone.
Any router that does not support IPoE/IPv6 on the internet in Japan does not get priority routing at crucial exchange points between local area lines, the ISP, and the NTT backbone. PPPoE is worthless because PPPoE/IPv4 in Japan is ‘tapped out’ and sits in a traffic jam on the local internet highway on-ramp while IPoE/IPv6 get priority and whizzes by on the IPv6 super highway.
Japan Internet Setup
Do yourself a favor and do not waste time and money with any WiFi router that does not support DS-Lite/Map-E protocols and IPoE/IPv6 service. Completely eliminate all PPPoE on your home network if you want fast internet service in Japan.
The first step: get a free IPv6 service option. All of the Japanese internet providers offer free ‘v6 Plus’ or ‘IPoE’ or similar sounding service options for connecting your home internet directly with IPv6. This is easy to do by phone or online.
The second step: get a WiFi router that supports DS-Lite and Map-E. Either rent a pre-configured WiFi router from your internet provider or purchase one. The major Japanese WiFi home router manufacturers all support these protocols and maintain IPv6/IPoE lists of internet providers and services qualified with their WiFi routers:
Only purchase the latest WiFi models and make sure the device is updated with the latest firmware. Also make sure that PPPoE bridging functions are turned off.
If you are not a DIY networking guru, save time by renting a pre-configured WiFi router from your Japanese internet service provider. Rental prices vary, So-Net for example charges ¥400 a month. If you are in Japan for the long-term and futzing with internet configurations is not a problem, a good WiFi router investment from the list above can save you money.
UPDATE June 2020
NTT FLETS is was experiencing speed stress from people working at home during the start of the COVID crisis. If you have not done so already, migrate from PPPoE IPv4 to IPoE IPv6. Otherwise peak internet hours will be unbearably slow. A good stress free IPv6 service is KDDI au Hikari nuro which uses excess bandwidth that KDDI rents directly from NTT dark fiber exclusively for nuro.
UPDATE December 2021
I picked up a Buffalo WSR-5400AX6S WiFi mesh router and it worked very well out of the box. The only thing I changed was setting my own SSID and network password.