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half-duplex cable modem fun

So, I _finally_ (1.5 years after initial request) got cable TV and a
cable modem installed at my house in the woods. Proffered the usual
win98 sacrificial cow to the installer, who got it running there. Now
I'm trying to get my firewall (formerly serving a dial-on-demand modem
connection) configured to run on the thing.

It's a half-duplex setup; cable modem down, phone modem up.
Configuration was very straightforward under win98 (he didn't even dump
an annoying branded web browser on me); basically I set up the ethernet
card as and set the dialup connection with the usual
name/password etc. There are two login names with the same password; one
allows me to use a simple two-way modem connection; the other sends the
downstream packets through the cable modem instead. DNS is apparently
magically resolved via PPP.

Here's the obligatory firewall question: are there any tricks to setting
up IP masquerading on a half-duplex setup like this? It seems like it
would either be really simple ("just work") or it would be
nigh-impossible. I'm pretty familiar with IP masquerading from dial-up,
DHCP, etc.

I'm also having trouble just getting the analog modem end running;
perhaps someone can help me with this.

I finally gave up last night after banging my head on the dialup for
awhile. It's weird - I'm pretty sure it uses PAP, and I've configured it
as such (most of the entries in the cable-modem howto on this also
mention PAP, and when I click "more info" on the running win98
connection it says "Password Authentication Protocol" (shouldn't it be
"Peer Authentication Protocol"? whatever).

But when I try to bring up the link, I get a ton of debug messages and a
loopback warning that as far as I know indicates that I'm triggering PPP
to early (the chatscript isn't complete).

Most of the example chatscripts I've seen have the following last lines:
''        ATDT7777777

But this never completes for me, times out (I never get a CONNECT)

The weird thing is this: running hyperterminal under windows (9600 baud
modem, same one used to setup the connection originally) I can dial in,
and it says 


and then spews out a little banner and asks for a password (no

But from my firewall, using minicom, I never get a CONNECT message. I
can dial in without trouble to Mindspring from the same minicom session,
and it connects, asks for username/password, etc. But when I try to dial
the cable modem ISP's number, it dials, sits there, and if I ever type
anything it just says NO CARRIER.

I'm going to try swapping modems tonight, but I don't have much
confidence in that.

I realize this is more of a modem/ppp question than a firewall question,
and I'll gladly send it over to debian-user if it's more appropriate


Paul Reavis                                      preavis@partnersoft.com
Design Lead
Partner Software, Inc.                        http://www.partnersoft.com

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