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FLET'S NGN Basics

This documentation is still being edited and may differ from the actual version.

Understanding the “hierarchical structure” of Japanese broadband and the characteristics of NGN (Next Generation Network) will help you realize why Flet’H tunneling is necessary.

The Three Layers of Providers

Section titled “The Three Layers of Providers”

In Japan, the broadband service you use is typically provided by three companies playing different roles:

LayerRoleTypical ExamplesResponsibilities
Layer 1: InfrastructureNTT (FLET’S)NTT East / WestProvides physical fiber and the NGN closed network.
Layer 2: GatewayVNEJPNE, BBIX, OCN, Asahi NetOperates the tunnel gateways (AFTR / BR) to the internet.
Layer 3: Brand/RetailISPBiglobe, So-net, @nifty, OCNHandles billing, support, and provides PPPoE accounts.

Why does this matter? Because your ISP often does not operate its own tunneling equipment. For example, you might subscribe to ISP A, but they rent infrastructure from VNE B. Flet’H focuses on Layer 2 (VNE) because it determines which technology (MAP-E or DS-Lite) you must use.

NGN: A “Pure IPv6” Closed Network

Section titled “NGN: A “Pure IPv6” Closed Network”

A common misconception is that a fiber connection automatically means internet access. The NGN connection state goes through several phases:

  1. Pre-contract / During Activation: Your IPv6 address/prefix belongs to the NTT infrastructure segment. You can only access NTT’s official network (e.g., flets-east.jp or flets-west.jp).
  2. Waiting for ISP/VNE Activation: In this phase, you are within the “NGN closed network.” While you cannot access the internet, you can communicate (e.g., ping) over IPv6 with other NTT NGN lines within the same region (East or West) that are in the same state.
  3. Fully Connected: Once ISP/VNE configuration is complete, your IPv6 traffic formally connects to the internet through a tunnel gateway (BR/AFTR).

Core Characteristics:

  • NGN is IPv6-only: The NTT NGN network itself does not support IPv4 at all. It is a massive, nationwide, pure IPv6 local area network.
  • No “Public IPv4” at the NGN level: You cannot obtain a public IPv4 address directly from the NGN layer.
  • IPv4 is a “Guest”: To allow access to IPv4 websites, VNE operators leverage the NGN IPv6 foundation, encapsulating IPv4 traffic into IPv6 packets (tunneling technology) for transport.

Flet’H’s Role: On this IPv6-only NGN network, Flet’H automatically finds the correct VNE tunnel endpoint to “connect” your IPv4 traffic to the outside internet.

Why IPv6 Must Work First

Section titled “Why IPv6 Must Work First”

Since NGN is a pure IPv6 network, IPv6 acts as the “highway” that carries the IPv4 tunnel. If the highway is not built (the wan6 interface has not acquired an address), the tunnel (Flet’H IPoE interface) cannot be established. This is why we emphasize configuring wan6 first in our tutorials.

For how to pass IPv6 from wan6 to LAN clients, see LAN IPv6 Basics.

References

Section titled “References”