Julien Vehent on 11 Dec 2010 06:46:11 -0800


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Re: [PLUG] Comcast Cable modem & DHCP

I get an IP on the 68.0.0.0/22, and you seem to be on a private 10.1.10.0/24 network, so I assume you commercial account works differently.
However, since 10.0.0.0/8 is class A private network, non routable on the internet, I'm wondering: what is your public ip address here ?
Or do you double NAT you packets ? Once on your linux box and then on the comcast router again ? 



On 12/11/2010 09:34 AM, Casey Bralla wrote:


I am doing something very similar on my comcast commercial account.  I plug a
Debian computer into one of the network ports on the comcast modem and use
this as a firewall and router to my DMZ and internal network.

Originally, I had allowed the modem to assign an address with dhcp, but l then
switched to setting the IP statically (I don't remember why).  I assign
10.1.10.2 to the interface on my Firewall box, with a gateway of 10.1.10.1.  I
also use the comcast modem as a DNS server (10.1.10.1).

I then use Shorewall as my firewall, which routes packets to 2 other network
interfaces on my firewall box.

My /etc/network/interfaces file is:

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
# allow-hotplug eth0
# auto eth0
# iface eth0 inet dhcp


auto eth1
iface eth1 inet static
         address 192.168.2.1
         netmask 255.255.255.0
         broadcast 192.168.2.255
auto eth2
iface eth2 inet static
         address 192.168.1.1
         netmask 255.255.255.0
         broadcast 192.168.1.255

auto eth0
iface eth0 inet static
         address 10.1.10.2
         netmask 255.255.255.0
         broadcast 10.1.10.255
         gateway 10.1.10.1

(Note the commenting out of the dhcp lines.. wish I remember why I did this)



Hope this helps and welcome to the USA!







On Saturday 11 December 2010 9:08:44 am Julien Vehent wrote:

Hello Plug,

I just arrived in Philly (and thus joined the plug mailing list) and I'm
discovering comcast cable equipment (big motorola modem with one ethernet
plug).

I would like to replace the old linksys we are using in the house with a
Debian box connected to the modem (I want netfilter and traffic control).
The linksys is getting it's IP in DHCP mode already. From what I see, the
lease is 3 days long.

I thought a simple "dhclient eth1", the interface where the cable modem is
plugged in, would do the job, but it seems that it's refusing to give my
Debian a lease...

Here and there I read that a specific hostname should be provided by the
client, but AFAIK there is no such setting on the actual linksys.

I'm from france, and never used comcast or a motorola cable modem before.
This one is pretty old (I'd say 2004/2005) but still working fine so
replacing it is not an option. Also, I sniffed the DORA from the linksys
to the modem and didn't find anything specific in the packets.

So, I seek for your help. Is there any comcast black magic ritual necessary
to make this work ? Anybody using a linux box behind a cable modem with
dhcp ?

Thanks,
Julien

___________________________________________________________________________
Philadelphia Linux Users Group         --        http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
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___________________________________________________________________________
Philadelphia Linux Users Group         --        http://www.phillylinux.org
Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce
General Discussion  --   http://lists.phillylinux.org/mailman/listinfo/plug