🚀 go-pugleaf

Przemek Klosowski <przemek@rrdjazz.nist.gov> wrote in article
<541zvk3gx8.fsf@rrdjazz.nist.gov>...
> My local cable company is going to offer a cable modem capability,
> soon.  The speed is supposed to be around 1MB/s but unfortunately they
> initially are deploying a one-way system: 
> 
> How would one go about setting up  a Linux system to route outgoing
packets
> via the PPP interface, while receiving the incoming traffic via Ethernet?

You need to enable routing in the kernel, then you setup your ethernet and
ppp link up as normal (you'll need two IP addresses, one for the ppp link
and one for the ethernet link). After that you send packets via ppp, and
the service returns them back to you via the ethernet link (as if they were
routed via a different route). The enabled routing switch in the kernel
makes sure that the linux box will pick up ethernet packets that it can
route, which it then determines is actually meant for it.

The only thing I don't know is whether the return link is actually a normal
pucker ethernet link.

Chris Cradock 

Przemek Klosowski  <przemek@rrdjazz.nist.gov> wrote:
[...]
> How would one go about setting up a Linux system to route outgoing
> packets via the PPP interface, while receiving the incoming traffic via
> Ethernet? Can it be done by simply setting up some static routes, or
> would it require patches to the network stack? Without having studied the
> appropriate pieces of the kernel, i'd guess that similar functionality is
> needed for net load balancing, where packets also are split across
> several net interfaces.

I suspect just configuring the ethernet driver with ifconfig, but not
adding a route for it would allow incoming packets to enter the TCP/IP
stack, and have PPP call in normally, and set up its default route. If your
ISP also sends data via PPP, this is a bonus.

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Przemek Klosowski <przemek@rrdjazz.nist.gov> writes:

> My local cable company is going to offer a cable modem capability,
> soon.  The speed is supposed to be around 1MB/s but unfortunately
> they initially are deploying a one-way system: only download packets
> go over the cable---the uplink is via a a regular modem.  BTW, the
> cable modem has 10BaseT interface, which then goes to the Ethercard
> in the PC.

It should work fine with linux. See Phil Karn's web page for info on
using linux with the roadrunner cable modem service. All you have to
do is point your default route to the right place and you may have to
configure DHCP client software if they dont offer static IP addresses.

> How would one go about setting up a Linux system to route outgoing
> packets via the PPP interface, while receiving the incoming traffic
> via Ethernet?

You don't do any of that. The external box takes care of all that. All
you have to do is send it ethernet frames.

> Can it be done by simply setting up some static routes, ...

With an external box you just point default at the address they give
you. It could either be the address of the cable modem if it is a L3
(IP layer) device or the address of the router at the headend if it
is an L2 (MAC layer) device.

The GI external modem is an IP layer device. LANcity modems are MAC
layer devices. There are also many other vendors, but they all fall
into one of those categories.

> ... or would it require patches to the network stack? Without having
> studied the appropriate pieces of the kernel, i'd guess that similar
> functionality is needed for net load balancing, where packets also
> are split across several net interfaces.

If it was an internal modem (like the GI surfboard) you would be
screwed. First you would have to write a driver for the card (good
luck getting the programming info), then you would have to hack the IP
stack because those setups only use 1 IP address (the surfboard
doesn't have an IP address as far as the host is concerned).

HTH,

Joel Gallun (former cable modem engineer)

Przemek Klosowski <przemek@rrdjazz.nist.gov> writes:


>How would one go about setting up  a Linux system to route outgoing packets
>via the PPP interface, while receiving the incoming traffic via Ethernet?

It was MY understanding you just connected 10BaseT to the
cablemodem, and *it* had the phone line & cable connected to it...

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