Comcast Cable modem on linux? Anyone get it to work?

(Note: I did post this to alt.os.linux but now realize that this is a
more appropriate newsgroup. Please forgive the multiposting.)

Please give me a break on using google, comcast has limited newsgroup
access to 2Gb a month, I did not know and burned it all up the first
night because it was so fast. Wow. Now no access till the month is over
and I need Linux help.

I have a comcast account and want to connect with my Fedora box like I
did with my DSL account. I read that Comcast uses dhcp and that is what
I use to connect with now. I added to my
/etc/sysconfig/network-scripts/ifcfg-eth0 to use dchp on Ethernet and
from what I read, I need to put my Comcast dhcp_hostname in there and
it is some kind of cc name. I have no idea where to find this cc name
in windows but when I exceeded my bandwidth on Usenet, I got back an
error message from my newsreader of this and the cc hostname was there,
but it was a really long name, 33 characters including the cc in the
front. I am not sure if all of this is what I need to log on to comcast
with my Linux machine now.

When I try by doing as root, service network restart, the system brings
down eth0 and brings it back up again and it seems to work. I can then
use ifcofig to see that I really do have a valid Internet IP address
but nothing is reachable. I then looked at the route with the route
command and when I first try to restart the network, I get a default
route for eth0 but nothing is reachable. No domains can be found, DNS
apparently is not working, I cannot ping anything on the net either
because it is not reachable. I can ping myself, localhost, and my eth1
IP of 192.168.0.1.

After about a minute or so, I notice that my default route disappears
from the route command and I no longer have a default route. Not that
it works anyways. I don't really know what is going on, I think that
maybe I do not have the "cc" name for dchp hostname correct or I am not
being logged in somehow. How would I find out what is happening when I
try to start the network and eth0 connects? Is there a system log that
I can use tail on when I try to connect? How can I find out for sure
what my cc dchp hostname really is when I do log in with Windows XP?
What is really needed to log into a cable modem on Comcast with Linux?

Somebody out there must already have this working, how in the world do
you connect with Comcast on a Linux box?

So really, can someone that is able to get on Comcast with a cable
modem please tell me how it is done? I have googled my ass off on this
and have not really been able to come up with anything other than I
need dchp and installed the rpm package, dchp-3.0.1-11. I also need to
put in a dhcp hostname in ifcfg-eth0 and it is some kind of cc name. I
am connected right now on an XP computer but really want to get my
Linux box back online, being the gateway again and have it do the
connecting and then I can ipforward and masquerade to share the net
with my other computers via hub on eth1 like the old days of adsl. I
used the roaring penguin adsl-start command to get online with ADSL and
PPPoE but this Comcast stuff has me stumped.

Somebody please help!

Thank you,
Ohmster
(Please forgive the google posting, I will get back to slrn when my
Linux box is back online and I get more bandwidth from Comcast. I will
check back for answers, reports, and praise, I promise!)

> I have a comcast account and want to connect with my Fedora box like I
> did with my DSL account. I read that Comcast uses dhcp and that is what
> I use to connect with now. I added to my
> /etc/sysconfig/network-scripts/ifcfg-eth0 to use dchp on Ethernet and
> from what I read, I need to put my Comcast dhcp_hostname in there and
> it is some kind of cc name. I have no idea where to find this cc name
> in windows but when I exceeded my bandwidth on Usenet, I got back an
> error message from my newsreader of this and the cc hostname was there,
> but it was a really long name, 33 characters including the cc in the
> front. I am not sure if all of this is what I need to log on to comcast
> with my Linux machine now.

I have a Linux host and I connect with Comcast by DHCP. Debian doesn't use
/etc/sysconfig (AFAICT), so I don't know about that, but I use dhcp3-client
and it works just fine. It starts when the network comes up because I have
the following in /etc/network/interfaces:

auto wan
iface wan inet dhcp

(My outward facing interface is named wan.) See interfaces(5). With that
set up, ifdown eth0 ; ifup eth0 should restart your DHCP client.

> When I try by doing as root, service network restart, the system brings
> down eth0 and brings it back up again and it seems to work. I can then
> use ifcofig to see that I really do have a valid Internet IP address
> but nothing is reachable.

What IP address is it? Send us the output of ifconfig eth0. If DHCP is
failing to acquire a lease, it may assign a placeholder IP address
(169.something-- can't remember now) that's invalid.

> I then looked at the route with the route
> command and when I first try to restart the network, I get a default
> route for eth0 but nothing is reachable. No domains can be found, DNS
> apparently is not working, I cannot ping anything on the net either
> because it is not reachable. I can ping myself, localhost, and my eth1
> IP of 192.168.0.1.

OK, I have

$ route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use
Iface
lan * 255.255.255.0 U 0 0 0 lan
69.140.168.0 * 255.255.248.0 U 0 0 0 wan
default c-69-140-168-1. 0.0.0.0 UG 0 0 0 wan

$ route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use
Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 lan
69.140.168.0 0.0.0.0 255.255.248.0 U 0 0 0 wan
0.0.0.0 69.140.168.1 0.0.0.0 UG 0 0 0 wan

> After about a minute or so, I notice that my default route disappears
> from the route command and I no longer have a default route.

OK, I haven't seen this happen before, but it sounds as though DHCP is
failing to acquire its lease, and then giving up and removing the route.

> Not that
> it works anyways. I don't really know what is going on, I think that
> maybe I do not have the "cc" name for dchp hostname correct or I am not
> being logged in somehow. How would I find out what is happening when I
> try to start the network and eth0 connects? Is there a system log that
> I can use tail on when I try to connect?

If you run ifdown eth0 ; ifup eth0 from the console, DHCP should log its
progress messages there, and you can see what's happening. Check the man
page for your DHCP client to see you can increase the verbosity. Also look
to see where it logs to, but it's probably a combination of stdout/stderr
and /var/log/syslog.

> How can I find out for sure
> what my cc dchp hostname really is when I do log in with Windows XP?
> What is really needed to log into a cable modem on Comcast with Linux?

You don't need to specify your hostname in order to acquire a DHCP lease.
It's the other way around: you can either ask Comcast to send you the name
as part of the negotiation, or override it with a different one. But
neither of those is required.

FWIW, once you have an IP address, you can use the 'host' command to find
its hostname: in my case,

$ host 69.140.175.73
73.175.140.69.in-addr.arpa domain name pointer
c-69-140-175-73.hsd1.md.comcast.net.

Based on everything you've said, it sounds as though your DHCP client is
failing to acquire a lease, and now you just have to figure out why. It
shouldn't be too hard, and you have some options:

- Have you changed the NIC that faces your cable modem? If so, you may
need to reboot the modem (which in my case means unplug, wait 30 sec., then
plug it in again). Some cable modems acquire the MAC of the NIC they're
talking to, and if that MAC changes they don't function until you reboot
them. Probably worth a try even if you haven't changed the NIC.

- Maybe your NIC is bad. Try plugging the cable modem into a different one
(e.g. your LAN one). Then of course you'll have to reconfigure your
network and reboot the cable modem.

- Call your local Comcast office, and follow the options to get through to
internet tech support. They can tell you if they have a clear connection
as far as your cable modem, and if it's operating properly. You'll have to
judge whether to tell them that you're running Linux, though.

--
To reply by email, change "deadspam.com" to "alumni.utexas.net"

On comp.os.linux.networking, in
<(E-Mail Removed) .com>,
"Ohmster" wrote:

Hello Ohmster,

> (Note: I did post this to alt.os.linux but now realize that
> this is a more appropriate newsgroup. Please forgive the
> multiposting.)

I was going to crosspost my pitiful response here.

>
> Please give me a break on using google,

This is the sort of thing it should _only_ be used for, but
you really should put a name in your From header.

> comcast has limited
> newsgroup access to 2Gb a month,

Holy Bandwidth, Batman! You trying to mirror the Usenet?

> I did not know and burned it
> all up the first night because it was so fast. Wow. Now no
> access till the month is over and I need Linux help.
>

<snip>

Never done anything but PPP, but it looks Andrew Schulman has you
covered. I'm just being a student on this thread.

But if you _really_ want to see the unfiltered and complete
details of what's going through the interface, use tethereal
(textmode). Run as root. Happens too fast to read realtime, so
save to a file.

(Use -p to keep it out of promiscuous mode so that it will
only capture traffic to and from your interface. If you run in
promiscuous mode, be sure to close tethereal before you shut down
the interface.)

# tethereal -p -i eth0 -w file

To read it for a quick look:

# tethereal -r file | less

For all the details (tree display of packets):

# tethereal -V -r file | less

This is also interesting:

# strings file | less

Good luck,

Alan

--
If you replied to an article of mine and are wondering
why I didn't respond to you, the fact is that I didn't
even download your article. For an explanation, see:
http://home.earthlink.net/~alanconnor/newsfilter.html

Andrew Schulman <(E-Mail Removed)> wrote in
news:(E-Mail Removed):

> I have a Linux host and I connect with Comcast by DHCP. Debian
> doesn't use /etc/sysconfig (AFAICT), so I don't know about that, but I
> use dhcp3-client and it works just fine. It starts when the network
> comes up because I have the following in /etc/network/interfaces:

Andrew,

This looks like a good read and I will get back to this after dinner and
for sure save the post for my archive of things I need to know. I just
wanted to let you know that I got online last night with bit twister's
help in alt.os.linux. I had mutiposted this to the two newsgroups and he
came to the rescue, same post in the other group. Here are the configs
that I used to get me online. No hardware or cabling changes were
necessary since losing my ADSL connection.

[root@ohmster sysconfig]# cat network
NETWORKING_IPV6=no
NETWORKING=yes
GATEWAYDEV=eth0
HOSTNAME=ohmster.com
[root@ohmster sysconfig]#

[root@ohmster network-scripts]# cat ifcfg-eth0
DEVICE=eth0
ONBOOT=yes
BOOTPROTO=dhcp
USERCTL=no
PEERDNS=yes
PEERYP=no
PEERNTPD=no
TYPE=Ethernet
IPV6INIT=no
DHCP_CLIENT=dhclient
NEEDHOSTNAME=no
NETMASK=255.255.248.0
[root@ohmster network-scripts]#

The netmask I got from my XP box when online with Comcast. I just right
clicked on Network Places and got Properties, then double clicked on my
LAN connection and found the netmask in there and used it for Comcast on
Fedora Core 3. It all worked beautifully.

Thanks for your help, I will be back after a while.

--
~Ohmster

On Sat, 16 Sep 2006 01:12:06 +0000 (UTC), Ohmster wrote:

> The netmask I got from my XP box when online with Comcast. I just
right
> clicked on Network Places and got Properties, then double clicked on
my
> LAN connection and found the netmask in there and used it for Comcast on
> Fedora Core 3. It all worked beautifully.

or click up a cmd/Prompt doze terminal and do a
ipconfig -all 8-)