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

[Ferdinand Schmid]

Your assumption about DHCP is correct IIRC.  I don't know why I couldn't get
the modem to give me an IP address - but then my sample is one modem.  Comcast
was less than helpful when I called and stated that this would be my problem,
not theirs.  

I do know, however, that my computer works with my own dhcp servers.  That's
what I use every day, no matter if I boot Linux (99.99% of the time) or the
few times per year that I boot WinXP.  With the Comcast modem I couldn't get
dhcp to work using either OS.

Ferdinand

--On Monday, March 15, 2004 10:23:07 AM -0700 Chip Atkinson <chip at rmpg.org>
wrote:

> Dang.  Ok.  I'll have to see if I can round up a windows machine for a
> little while.
> 
> About the DHCP, that is on the cable end of the modem, so I shouldn't have
> to worry about that, right?
> 
> Thanks for the information too.
> 
> Chip
> 
> On Mon, 15 Mar 2004, Ferdinand Schmid wrote:
> 
>> Chip:
>> 
>> You will need to use Internet Explorer to get to the registration site for
>> Comcast.  I have gone through this exercise and found that they really
>> require IE.  Also - dhcp in their cable modems doesn't necessarily work with
>> every computer.  I had a terrible time with it on my PC - couldn't get it to
>> work on a Dell laptop under Linux or Windows.  However, a D-Link router was
>> able to talk to it.  Strange...  So my approach to get it working was to use
>> a USB cable combined with a Windows PC to do the modem registration.  Until
>> this is complete you will only be able to get to your cable modem and to
>> Comcast's DNS servers.
>> 
>> So - find a Windows PC to register the modem and then connect your Linux
>> system.  If you can't get dhcp working with your particular modem then just
>> pick your IP address manually.  The default route (your cable modem's local
>> IP) never changes anyway.
>> 
>> Ferdinand
>> 
>> --On Monday, March 15, 2004 08:25:44 AM -0700 Chip Atkinson <chip at rmpg.org>
>> 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
>> > 
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>> 
>> 
>> 
>> --
>> Ferdinand Schmid
>> Architectural Energy Corporation
>> Celebrating over 20 Years of Improving Building Energy Performance
>> http://www.archenergy.com
>> 
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> 
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--
Ferdinand Schmid
Architectural Energy Corporation
Celebrating over 20 Years of Improving Building Energy Performance
http://www.archenergy.com