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

[John Hernandez]

Well, my info is probably outdated.  I wouldn't be surprised if they've 
gone to a routed/NAT configuration for security reasons.

Chip Atkinson wrote:

>Hmmm... thanks.  I know my modem has two IP addresses, a LAN and a WAN.
>That may be the configuration out of the box but not necessarily the
>correct one.  Maybe that's why I have to run the setup software that they
>provide...
>
> On Mon, 15 Mar 2004, John Hernandez wrote:
>
>  
>
>>Chip, AFAIK, those modems are usually set up in bridging mode, which
>>means your PC will need to send out the DHCP request.  As I recall, it
>>also required you to send a hostname along with the request.  I'm not
>>sure if that is still the case, as my connection was on the old ATTBI
>>network.
>>
>>Chip Atkinson 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
>>>>>
>>>>>_______________________________________________
>>>>>Web Page:  http://lug.boulder.co.us
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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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>>>
>>>
>>>
>>>      
>>>
>>    
>>
>
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>  
>

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