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My Rakuten Hikari line suddenly became extremely slow, so I enabled IPv6 connectivity.
\nIn this article, I configure it using a Buffalo router, the WSR-5400AX6.
\n(I think most Buffalo home routers probably use roughly the same settings…)
\n\nI have been using Rakuten Hikari since about half a year ago (around September 2020).
\nI had moved to primarily working remotely, wanted a stable line at home, and Rakuten Hikari also happened to be running a one-year free campaign, so I signed up for it.
\nAnother big reason was that, since I live in a rental, it could be activated without any work that would require drilling holes in the wall.
\nAlthough I had a few complaints—such as never being able to get through on the phone to apply, and it taking about two months from the application to activation—after it was opened I was consistently getting around 200–400 Mbps on Fast.com (IPv4, wired), so it was very comfortable to use.
\nIn my environment, because I did not know much about IPv6 and was not confident I could configure it properly, and because I was already getting fully satisfactory speeds with IPv4-only connectivity, I had disabled IPv6 in the router settings and configured it to reject all IPv6 connections from the internet side.
\nHowever, around January 18, 2022, the connection suddenly became slow.
\nSpecifically, line speed fell to around 75 Mbps during the day and around 2–8 Mbps at night. (These are both Fast.com measurements over IPv4 on a wired connection.)
\nI tried the usual things, such as restarting the modem, router, and OS, but the situation did not improve, so I decided to enable IPv6 connectivity to improve communication speed.
\nRakuten Hikari uses a service from Arteria Networks.
\nTherefore, to enable IPv6 internet connectivity on a Rakuten Hikari line, you need to use a mechanism called Cross Pass provided by Arteria Networks.
\nReference: Broadband Access (Cross Pass) | Arteria Networks Corporation
\nTo enable the Cross Pass feature, your router must support Cross Pass settings.
\nFor Buffalo routers, you can check which router and firmware versions support Cross Pass at the following link.
\nReference: Verified list of devices compatible with IPv6 (IPoE/IPv4 over IPv6) | Buffalo
\nIn the case of the WSR-5400AX6, support starts with the current latest firmware version, Ver.1.02 or later, so update the firmware if necessary.
\nIf the [IP Address Acquisition Method] setting is not shown and only “The IP address acquisition method is set to ‘Use Internet @ Start’” is displayed, the switch on the back of the router body is set to [Auto] rather than [Manual].
\nIn that case, set the switch on the back of the router to [Manual].
\nThis enables IPv6 connectivity when connecting to the internet.
\nYou can check whether IPv6 internet connectivity is enabled by seeing whether [via IPv6] is displayed in the header of the following site.
\nReference: IPv6-enabled services | Arteria Networks Corporation
\nNext, let’s check the ND proxy setting used with IPv6.
\nUnlike IPv4, IPv6 does not use IP masquerading through NAT.
\nTherefore, depending on the router settings, it can become easy to access hosts on the home network directly from the internet side.
\nSince home-network devices are generally assumed to be used privately, leaving them accessible from the internet is undesirable from a security perspective, which shows how significant the security benefits of the NAT commonly used with IPv4 are.
\nThis time, because I am enabling IPv6 internet connectivity, I want to make sure devices inside the network cannot be accessed from the internet side.
\nTo implement that kind of environment, enable ND proxy in the router settings.
\nConfigure it as follows.
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