[lug] tcpdump, routing, ppp, and cable modem questions(s)

Chip Atkinson chip at rmpg.org
Mon Mar 15 08:25:44 MST 2004

Greetings all,

I recently signed up for internet access through Comcast, the cable TV
provider and am trying to get my machine connected to it.  During the
process I came across/caused a couple problems and also can't connect out
to anything past the cable modem.

Here are the problems:
1) the ppp0 interface has disappeared.  It was working that morning but
now is gone.
Using kppp I get an error saying
ppp: no such interface (don't remember the exact wording)
ifconfig ppp0 up
returns ppp0: unknown interface: No such device.

2) I was using tcpdump to watch network traffic on eth0.  When there was
no default route set, I saw tons of ARP requests from other machines, but
when I set the default route: route add default gw (the
cable modem's IP), the ARP request traffic wasn't visible suddenly.  When
I deleted the default route, the traffic was visible again.
I thought tcpdump grabbed all of the traffic, regardless of routing

3) I'm unable to get to a web server on the Comcast network to register
and get to the internet and I fear that it's due to something weird that
also caused ppp and the weird tcpdump behavior.  I can ping the WAN end of
the cable modem, but nothing else.

Does anyone have any similar experiences or ideas?  Right now I'm kind of

Thanks in advance.


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