Casey Bralla on 11 Dec 2010 06:35:05 -0800

[Date Prev] [Date Next] [Thread Prev] [Thread Next] [Date Index] [Thread Index]

Re: [PLUG] Comcast Cable modem & DHCP

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 to the interface on my Firewall box, with a gateway of  I 
also use the comcast modem as a DNS server (

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
auto eth2
iface eth2 inet static

auto eth0
iface eth0 inet static

(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         --
> Announcements -
> General Discussion  --


Casey Bralla
Chief Nerd in Residence
The NerdWorld Organisation
Philadelphia Linux Users Group         --
Announcements -
General Discussion  --