Re: comcast problem

On Wed, 18 Jan 2006 13:05:26 -0800, d wrote:

> hazzmat wrote:
>> This is not a Linux specific problem but I was hoping people with Comcast
>> experience could suggest some ideas...
>> My brother has had a working Comcast highspeed cable modem internet
>> service working with his Mac for months and months. Now it's not working
>> and I took a Linux system over (also win2k) to try to help diagnose the
>> problem.
>> In Linux the symptoms are these (and as far as I can tell, it's the same
>> with winblows). System set to dhcp (which i know works because I tested it
>> in my home network before schlepping it over), Linux gets an IP address
>> (69.something.something.something) it appears to get (according to 'route
>> -n') a default GW, and it gets 2 ISP provided nameservers, too. But no
>> pinging is possible. Not Comcast nameservers, not default GW address,
>> nothing. Switching ethernet cables, resetting modem, powercycling modem
>> makes no difference.
>> I know nothing about Comcast service
>> setup--nothing about what ethernet cables should be used between
>> "Scientific Atlanta" modem and NIC. I am assured that no special login
>> software is needed. According to tech support, says my brother, "Anybody
>> with a laptop should be able to come over, plug in and surf through the
>> modem." What should I be looking at?
>> --
>> Get Big Brother out of my email to reply.
> 1. Is the machine directly connecting to the cable modem?

I tried it that way(direct), and when direct connection to the cable
modem failed, I then tried plugging a netgear router in, which has been
used successfully at the location with the cable modem previously. (when
using the Netgear, the linux system got a 192.168.0.X address and could
ping the Netgear router, but nothing beyond. Nameserver and default gw
were successfully set by DHCP to the Netgear's internal IP address when
the Netgear was in the chain. Like I said, in a *normal* network context
the DHCP enabled connection of the Linux system works perfectly (windows
does too). In this context however with the Comcast connection all those
things get set up by DHCP in an apparently correct manner, but pinging and
nameresolution just do not work. It would seem that packets go into the
cable modem from our client end, but they aren't getting out. I tried to
ping an external machine at a fixed IP address, which was set to log ICMP.
Looking at the log I see that nothing came in from the Comcast network
block we were getting IPs from.

> 2. If not, and you have a router, reset the

>3. Does your Linux machine have iptables/ipchains on? 4. If so, turn the
service off.

There was no firewall script in place--all chains accept, no natting or
anything. This setup worked flawlessly just as it is in my home Linux
based network. When this system was booted into w2k there was a Sygate
personal firewall running, but again, that configuration also worked
flawlessly in my own simple network. There should be no reason that the
distribution's default iptables service would prevent the system from
using DHCP in any context, but if I get another chance to work at the site
tonight I'll trying flushing all iptables rules.

> What type of ping response are you receiving?

No response at all: 100% packet loss. (Unless the Netgear router is
interposed between the Linux box and the cable modem. Then as I mentioned
there is no problem when pinging the Netgear's LAN interface--but that's
is as far as it will go.)

Get Big Brother out of my email to reply.