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FLET'S PPPoE Basics

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

While Flet’H focuses on IPoE (IPv4 over IPv6), understanding the traditional PPPoE dial-up method helps you appreciate why switching to IPoE is beneficial.

What is PPPoE?

Section titled “What is PPPoE?”

PPPoE (Point-to-Point Protocol over Ethernet) is a technology for creating point-to-point connections over Ethernet. For FLET’S Hikari lines in Japan, it has been the most common way to access the IPv4 internet for the past two decades. Its defining feature is that it requires a username (ID) and password. The format is usually [username]@[isp-domain].com (e.g., h1ggy@fleth.link).

PPPoE Mechanics and MTU

Section titled “PPPoE Mechanics and MTU”

In NGN networks, a PPPoE connection is established between the user’s router and the NTT Network Group Interface (NGI). From the NGI, the connection is relayed to the ISP via an L2TP tunnel.

Due to this double encapsulation, the standard Ethernet MTU (1500) is effectively compressed.

[ Standard Ethernet Frame ]
| Payload (1500 bytes)                                          |
+---------------------------------------------------------------+


[ PPPoE + L2TP Encapsulation ]
| PPPoE(8B) | L2TP(38B) | Payload (1454 bytes)                  |
+-----------+-----------+---------------------------------------+
<---------------------- 1500 bytes ----------------------------->

After subtracting the PPPoE (8B) and L2TP (38B) headers from 1500 bytes, the actually usable payload size becomes 1454 bytes. In the Japanese FLET’S Hikari environment, it is common practice to set the MTU to 1454 for stable communication. Improper MTU configuration leads to packet fragmentation and reassembly, which is a major factor in reduced throughput.

Why is PPPoE Slow?

Section titled “Why is PPPoE Slow?”

You may find that even with a 1Gbps “Next” line, your PPPoE speed drops to single-digit Mbps during evening peak hours.

Physical Cause: NGI bottlenecks NTT’s rules dictate that adding NGI capacity depends on subscriber counts. With the surge in video streaming and large downloads, the processing capacity of these physical NGI units has reached its limit, creating a severe bottleneck.

Note: Urban legends regarding PPPoE There is a common claim on the internet that “ISPs are intentionally limiting investment in PPPoE to push users to IPoE.” This is widely considered an urban legend. While it is true that expansion rules are strict, there is no solid evidence to support the various speculations regarding the strategic intent of ISPs.

Current Status and Use Cases for PPPoE

Section titled “Current Status and Use Cases for PPPoE”

Despite its congestion issues, PPPoE is still useful in some cases:

  • Static IP: Many affordable static IP services are still provided via PPPoE.
  • Dedicated IPv4: If you need a fully dedicated public IPv4 address (not shared ports), PPPoE is the most direct method.
  • Multi-session: FLET’S lines typically allow two simultaneous PPPoE sessions (e.g., one for your ISP and one for the NTT portal). Furthermore, by subscribing to “Session Plus” (セッションプラス), you can support up to 5 simultaneous PPPoE sessions.

Summary

Section titled “Summary”

PPPoE has served Japan well for years, but it is struggling under the weight of modern internet traffic. The IPoE solution enabled by Flet’H is essentially designed to bypass the congested NGI equipment and unlock your fiber line’s true speed.

References

Section titled “References”