PPPoE in DSL modem/router (novice question)

[Allen Weiner]

I use Verizon DSL (in my location Verizon uses PPPoE). My modem is a
Westell 6100 modem/router. ( I have no additional networking hardware.)
My OS is Fedora 7 (Linux).

I would like to have a clearer understanding of which PPP functions are
integrated in my modem.

When I used to use dial-up, PPPD ("PPP daemon") was running in Fedora.
Now, with DSL, PPPD is not invoked. Fedora includes PPPoE software (from
Roaring Penguin Software). But this software is not being invoked on my
system.

PPPoE is running on my modem/router. Does the modem/router also run PPP?
I've read that PPP consists of a number of major states: establishing,
authenticating, networking, terminating, and dead. Is any or all of this
functionality integrated into the modem/router?

Additional questions:

1. Is the ethernet cable between my NIC and modem carrying strictly
ethernet frames, as if the PC were on a LAN with no Internet connection?

2. Is the line between my modem and phone jack carrying PPPoEoA frames
or just PPPoE frames?

3. Is there an information source (e.g. website, article, book) that
elaborates on this? The PPPoE RFC is of minimal help to me. It just
illustrates how PPP frames are encapsulated in ethernet frames.

[Doug McIntyre]

Allen Weiner <alweiner7@hotmail.com> writes:
>I use Verizon DSL (in my location Verizon uses PPPoE). My modem is a
>Westell 6100 modem/router. ( I have no additional networking hardware.)
>My OS is Fedora 7 (Linux).

>I would like to have a clearer understanding of which PPP functions are
>integrated in my modem.

>When I used to use dial-up, PPPD ("PPP daemon") was running in Fedora.
>Now, with DSL, PPPD is not invoked. Fedora includes PPPoE software (from
>Roaring Penguin Software). But this software is not being invoked on my
>system.

>PPPoE is running on my modem/router. Does the modem/router also run PPP?
>I've read that PPP consists of a number of major states: establishing,
>authenticating, networking, terminating, and dead. Is any or all of this
>functionality integrated into the modem/router?


Your question is really oddly worded. PPP over Ethernet is running in
my routers, does my router also run PPP? Since PPPoE is PPP over ethernet,
yes, its running PPP. Almost every router (as opposed to bridge or
"dumb modem") has PPP over Ethernet or over ATM or both built into.

It handles all phases and negotiation of the PPP protocol to talk back
to the ISP for you.

Yes, your workstation can also do PPPoE. So can every Windows and Mac box
out there. But they in general don't.


>Additional questions:

>1. Is the ethernet cable between my NIC and modem carrying strictly
>ethernet frames, as if the PC were on a LAN with no Internet connection?

Yes.

>2. Is the line between my modem and phone jack carrying PPPoEoA frames
>or just PPPoE frames?

It really depends on what you mean and what your ISP does. Most do run
their DSL networks on ATM. I'm not sure by what you mean with PPPoEoA.
There's PPPoE and there's PPPoA. Technically both run over the ATM
network. Or PPPoE can also run over straight ethernet network, but PPPoA
can't.

Seperate protocols. The main difference is PPPoE has an extra 8 byte
overhead on each frame, so if PPPoA is supported all around, its
generally preferred as it doesn't have that. PPPoE frames are still
going to be chopped up into ATM cells the same, so in general they are
the same protocol.

>3. Is there an information source (e.g. website, article, book) that
>elaborates on this? The PPPoE RFC is of minimal help to me. It just
>illustrates how PPP frames are encapsulated in ethernet frames.

Right, you keep posting questions and you're looking for the 10,000
foot picture with incredible detail, and people are telling you to
look at the source material to fill in the incredible detail.
There's not going to be a good source for you other than to keep posting.
Alot of what you are asking is just common experience in networking.

[Doug McIntyre]

Allen Weiner <alweiner7@hotmail.com> writes:
> I gotta believe that between all of the
> OReilly books, and the IEEE papers,and networking magazines, someone out
> there gives a detailed description of the architecture of residential
> gateways.

You have something like this..
http://www.ciscopress.com/bookstore/product.asp?isbn=1587050870

But I'm not sure its at the level you are looking for.

> Also, for dial-up modems, there used to be a number of
> enthusiast websites. I haven't seen something similar for DSL modems.

No, nobody dwelves that deep into it any longer. 90% of the DSL router
is the same as any other router. Then you have 10% being the DSL chipset
in it, which won't get into any gory details unless you read the ADSL
tech specs.

Nobody could build their own DSL router from the ground up, there's not
much point to anyway.

You could dig around the OpenWRT project support for DSL routers, and
there you could probably find data sheets and source code for doing
various things.

You'll have hundreds of thousands of lines of code to support an OS
and router functions, which is one reason not many would dive into
such a thing..