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Internet Connectivity in Japan

My Japanese Internet Setup

1 Gbps fiber connectivity via Rakuten Hikari ISP (Arteria network backbone) with NTT Flets physical infrastructure. Native IPv6 with DS-Lite tunneling for IPv4 connectivity, managed by an OpenWRT router.

Infrastructure Components

  • Physical Infrastructure

    NTT Flets Hikari provides the physical fiber optic line to the apartment. This is a shared infrastructure used by multiple ISPs in Japan through a wholesale model.

    • Technology: FTTH (Fiber to the Home)
    • Capacity: 1 Gbps synchronous
    • Provider: NTT East/West (infrastructure only)
    • Ownership: Fiber line owned by NTT, service by Rakuten

  • ISP Service Layer

    Rakuten Hikari provides the ISP service layer, utilizing Arteria Networks backbone infrastructure for actual connectivity.

    • ISP: Rakuten Hikari
    • Backbone: Arteria Networks (AS17506)
    • IPv6: Native via RA (Router Advertisement)
    • IPv4: DS-Lite tunnel (RFC 6333)

  • Customer Equipment

    ONU (Optical Network Unit) converts fiber optic signals to Ethernet, provided by NTT as part of the Flets service.

    • Function: Optical to electrical conversion
    • Output: 1000BASE-T Ethernet
    • IPv6: Passes through natively
    • Management: No configuration needed

  • Router Setup

    Linksys E8450 running OpenWRT for advanced networking features including DS-Lite support.

    • Model: Linksys E8450
    • Firmware: OpenWRT (latest stable)
    • CPU: MediaTek MT7622BV (2 cores @ 1.35 GHz)
    • Features: DS-Lite, IPv6, VLAN, QoS

Performance Characteristics

Real-World Performance

While the connection is rated at 1 Gbps, observed throughput typically reaches ~600 Mbps for both upload and download. This is more than sufficient for all home use cases including 4K streaming, video conferencing, and my self-hosted infrastructure.

IPv6 and DS-Lite Configuration

Understanding DS-Lite (Dual-Stack Lite)

What is DS-Lite?

DS-Lite (RFC 6333) is an IPv4 transition mechanism used by many Japanese ISPs. It tunnels IPv4 traffic through IPv6 to an AFTR (Address Family Transition Router) gateway, which then NATs it to the public internet.

Why DS-Lite? Due to IPv4 address exhaustion in Japan, ISPs provide native IPv6 but use DS-Lite for IPv4 connectivity without assigning each customer a public IPv4 address.

sequenceDiagram
    participant Device as 💻 Your Device
    participant Router as 🔧 OpenWRT Router
    participant AFTR as 🔀 AFTR Gateway
    participant Internet as 🌐 Internet

    Note over Device,Router: Local IPv4: 192.168.1.x

    Device->>Router: IPv4 packet (e.g., HTTP request)
    Note over Router: Encapsulates IPv4 in IPv6
    Router->>AFTR: IPv4-in-IPv6 tunnel packet
    Note over AFTR: Decapsulates and NATs
    AFTR->>Internet: IPv4 packet with AFTR's public IP
    Internet->>AFTR: IPv4 response
    AFTR->>Router: IPv4-in-IPv6 response
    Router->>Device: IPv4 response

OpenWRT DS-Lite Setup

OpenWRT has built-in support for DS-Lite tunneling via the LuCI web interface:

Configure via LuCI

  1. Navigate to Network → Interfaces
  2. Add a new interface (or edit WAN)
  3. Set Protocol to Dual-Stack Lite (RFC6333)
  4. Set DS-Lite AFTR address to dgw.xpass.jp (Rakuten Hikari's AFTR endpoint)
  5. Save and apply

That's it! IPv4 connectivity will work through the DS-Lite tunnel.

IPv6 Native Configuration

IPv6 works natively without any special configuration. The ONU provides IPv6 via Router Advertisement (RA), and OpenWRT automatically configures it. A /64 prefix is assigned for the home network.

Limitations and Considerations

DS-Lite Limitations

Port Forwarding: Not possible with DS-Lite as you don't have a dedicated public IPv4 address. All IPv4 connections are behind CGNAT (Carrier-Grade NAT).

Workarounds:

  • Use IPv6 for incoming connections (if supported)
  • Use VPN tunnel to a VPS with public IP
  • Use services like Cloudflare Tunnel or Tailscale
  • Combo of VPS tunnel + Tailscale (my approach)

My Self-Hosting Solution

I use a combo of Vultr VPS + Tailscale VPN: my home server connects to a Vultr VPS in Tokyo (with public IPv4 and IPv6) via Tailscale. The VPS runs HAProxy as a reverse proxy, forwarding traffic through the secure Tailscale mesh to services running at home.

See Infrastructure Overview for complete details.

Additional Resources

  • RFC 6333

    Official specification for DS-Lite (Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion)

    Read RFC 6333

  • OpenWRT Documentation

    Complete guide for OpenWRT DS-Lite configuration and troubleshooting

    OpenWRT DS-Lite Guide

  • IPv6 Transition

    Understanding IPv6 deployment and transition mechanisms in Japan

    JPNIC IPv6 Info

  • Rakuten Hikari

    Official ISP website (Japanese)

    Rakuten Hikari