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

[Hugh Brown]

On Mon, 15 Mar 2004, Chip Atkinson wrote:

> 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)
> and
> 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 192.168.100.1 (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
> tables.
>
> 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
> stumped.
>
> Thanks in advance.
>
> Chip


I use Comcast out in MD and don't use ppp at all.  The cable modem
provides an address via dhcp.  I have one of those cable/dsl firewall
routers that sits between the cable modem and my home network and it all
just works.

Hugh