PPPoEoA with Linux?

PPPoEoA with Linux?

Post by skris » Sat, 29 Nov 2003 00:39:18



Hi,

I am interested in finding out if PPPoEoA is possible with the
existing linux patches and code.

I am interested in knowing if it is possible for a SOHO router /
gateway, to initiate a PPPoE connection (for the user) and using the
DSL WAN connection send the PPPoE packets.(Please note that I
understand that we can do simple bridging using RFC 2684 if we receive
PPPoE packets on the LAN interface. I am only interested in finding
out how the data flow is for PPPoE packets generated inside the device
and then sent out on the ATM interface).

As per my understanding of the PPPoE stack available for Linux, PPPoE
payload is generated by the stack and then it calls an Ethernet driver
(eth0 or so) which then frames an Ethernet header over the PPPoE
payload.

But, when it comes to PPPoEoA, PPPoE payload packets instead of
sending to Ethernet driver should be sent to something like nas0
interface (br2684ctl created interface). But there is no Ethernet
header over this PPPoE payload now because nas0 will not do that?

Who should do this? Is there a need to write a small layer where we
frame the Ethernet header before passing the packets to nas0
interface?

Does Linux already support this kind of a requirement?

Correct me if I am wrong in any of the above assumptions.

Please give me any pointers or information you have in this regard.

Thank you in advance.
Krishna

 
 
 

PPPoEoA with Linux?

Post by Horst Knobloc » Sat, 29 Nov 2003 02:50:39



> I am interested in finding out if PPPoEoA is possible with the
> existing linux patches and code.

What do you mean with "PPPoEoA", PPPoE over ADSL/ATM?
If yes, this is possible.

Quote:> I am interested in knowing if it is possible for a SOHO router /
> gateway, to initiate a PPPoE connection (for the user) and using the
> DSL WAN connection send the PPPoE packets.

Yes, this is also possible. The IP packet is received on the
LAN Eth port, then routed. After this the IP packet is
encapsulated in a PPPoE frame, this is then put in an Ethernet
frame which is encapsulated according RFC2684, and transmitted
over the ATM VC via the DSL connection. (Note that this assumes
that your router has a built-in DSL Modem).

So on the LAN side of the router you have the following
protocol stack:

IP
Ethernet
10Base-T

on the WAN side you have:

IP
PPP / PPPoE
Ethernet
AAL5 (RFC2684)
ATM
DSL

If you don't have a built in DSL modem in the router, you
have the following protocol stack on the WAN side:

IP
PPP / PPPoE
Ethernet
10Base-T

In this case the ATM/DSL specifics are realized by the
external DSL modem (which implements Ethernet bridging)
connected to the WAN ethernet port of your router.

[...]

Quote:> As per my understanding of the PPPoE stack available for Linux, PPPoE
> payload is generated by the stack and then it calls an Ethernet driver
> (eth0 or so) which then frames an Ethernet header over the PPPoE
> payload.

This is correct, however it's only half of the story. You
still need to transmit the PPPoE/Ethernet frames to your ISP.
For this the PPPoE/Ethernet frame is sent via an external DSL
modem towards your ISP.

Quote:> But, when it comes to PPPoEoA, PPPoE payload packets instead of
> sending to Ethernet driver should be sent to something like nas0
> interface (br2684ctl created interface). But there is no Ethernet
> header over this PPPoE payload now because nas0 will not do that?

> Who should do this? Is there a need to write a small layer where we
> frame the Ethernet header before passing the packets to nas0
> interface?

If you have in your Linux box a DSL-NIC, then the Ethernet
frames need to be generated by the NIC's driver, right.
(As a side note you could also deploy PPP over the ATM
VC directly instead, then you don't need the Ethernet layer).

Quote:> Does Linux already support this kind of a requirement?

Yes, at least the "AVM Fritz! Card DSL" should do this,
the driver is from AVM itself. I guess there are also other
DSL-NICs supported by Linux which are capable of doing this.

Ciao, Horst
--
?When pings go wrong (It hurts me too)? E.Clapton/E.James/P.Tscharn