Re: [tlug] True Gigabit ISP in Tokyo?

[Curt Sampson <cjs@example.com>]

On 2019-02-15 10:29 +0900 (Fri), Jean-Christian Imbeault wrote:

> Searching on the internet I found the Reddit thread below that implies that
> Softbank is using a custom implementation of IPoE which forces you to use
> their box if you want gigabit speeds.
> 
> https://www.reddit.com/r/japanlife/comments/9146ya/internet_provider_asking_for_monthly_fee_to/

Oh, that is a great link! It has a few critical facts in one of the
repsonses which made everything click into place.

So here's the deal:

Your modem or fiber converter gives you an Ethernet connection into
NTT's internal network. You still need to talk to an ISP to carry your
packets to the Internet and bring back responses; NTT is just
responsible for getting your packets to that ISP.

Usually when using Ethernet you use standard RFC 894 encapsulation of
IPv4 packets into Ethernet packets; this is what you're using when you
run an Ethernet cable between your computer and a router or between
two computers. This can work at longer distances, too, such as between
your apartment and some NTT central office somewhere or even an ISP,
but it's still a "LAN" connection.

In the old days of modems of course there was no Ethernet or LAN
connection to them; it was just a point-to-point serial connection to
the modem, which basically extended that serial connection to another
modem at the other end which demodulated it and had a serial output
(or moral equivalant); so in the same way that Ethernet <-> Fiber <->
Whatever <-> Ethernet can be looked at, from the endpoints' view, as
"just an Ethernet connection," the modem-to-modem connection from the
endpoint view is "just a serial connection."

A point-to-point connection is quite different from an Ethernet: with
point-to-point there are only two nodes on the network so you don't
have to bother putting a destination address on the data you're
sending. This, and various other desirable features such as being
able to authenticate with a name and password ('cause who knows who's
calling in) meant that a different protocol, called PPP (Point to Point
protocol) was developed to encapsulate IPv4 on serial connections. (You
may also have heard of its ancestor, SLIP).

For various complex reasons I won't get into, when people starting
bringing Ethernet into homes rather than using telephones and modems,
the PPP protocol was still used to connect to an ISP, only they had to
make a variant of it that would run over Ethernet: PPPoE. One of the
various reasons was for authentication: the name and password you set
in your router is used as part of the PPPoE authentication process.
Once the PPPoE connection is up and running, your router encapsulates
IPv4 packets into PPPoE packets instead of RFC 894 Ethernet packets
and sends them off over this "virtual" point-to-point link.

When NTT introduced IPv6 in a big way, they dropped PPPoE for it and
instead changed how their network works: your Ethernet connection now
looks like it's connected directly to your ISP and you standard IPv6
over Ethernet encapsulation. Once facet of this change is that your
line is now configured ("hardwired," if you will) to connect to only
one ISP for IPv6; you can't, as I do with PPPoE, set up multiple
connections to multiple ISPs.

This is where the connection speed issue comes in. I don't recall who
I was talking to a few months ago about this, but apparently the
hardware that terminates the PPPoE connection can't move data for any
particular connection faster than about 300 Mbps or so. So it doesn't
matter if your link to that hardware is faster: that device limits the
speed.

The IPoE connections, since they don't go through that hardware, don't
have the speed limitation. However, since IPoE is used only for IPv6,
only your IPv6 connections will be fast; if the site you're connecting
to doesn't support IPv6 you'll fall back to IPv4 which in the usual
case would still be over your PPPoE connection.

Softbank fixed this problem by, instead of sending IPv4 packets over
PPPoE, encapsulating them in IPv6 packets and sending them over the
IPv6-over-Ethernet connection. Works great, but of course you need a
router than knows how to do that sort of encapsulation and is
configured to do so. From the thread you linked, it sounds like what
they're doing is standard enough that you could convince another
device to do this, perhaps even a Linux box.

A (Japanese) friend told me that he'd heard that NTT will also offer
IPv4 over Ethernet connectivity in the same way that they do for IPv6,
but it's only available for businesses. That would solve the IPv4
speed problem.

On 2019-02-15 10:52 +0900 (Fri), Jean-Christian Imbeault wrote:

> Can you use your own router with Asahi or do you need to use an Asahi box?

>From reading Asahi's pages, it sounds as if you continue to use PPPoE
for IPv4 connectivity, so your own router should be no problem at all
so long as it will either also route IPv6 and provide NAT for the
internal network hosts or just do a straight pass-through of the IPv6
over Ethernet packets.

I'm curious if multiple devices work over the IPv6 connection when
it's just plugged into the local LAN. I.e., if you don't want to use
IPv4, can you just plug the NTT modem/DSU/fiber converter into the
Ethernet switch that all your home computers are using and all of them
(that support IPv6) will just work, each getting its own address?

cjs
-- 
Curt J. Sampson      <cjs@example.com>      +81 90 7737 2974

To iterate is human, to recurse divine.
    - L Peter Deutsch