Casey Bralla on 11 Dec 2010 06:56:51 -0800

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Re: [PLUG] Comcast Cable modem & DHCP

On Saturday 11 December 2010 9:46:01 am Julien Vehent wrote:
> I get an IP on the, and you seem to be on a private
> network, so I assume you commercial account works differently.
> However, since is class A private network, non routable on
> the internet, I'm wondering: what is your public ip address here ?

My public IP is, which is assigned by comcast to the modem via 
dhcp.  The modem in turn then does NAT to a private subnet 10.1.10.x which I 
connect to my Debian firewall box.  I then re-NAT this to 2 different private 
subnets (192.168.2.x to my DMZ and 192.168.1.x to my internal network).

BTW, I did not buy a "static" IP form comcast, but I find the DHCP IP is 
essentially static (years!) as long as you don't change the MAC of the 

> 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.
> >> 
> >> 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...
> >> 
> >> Thanks,
> >> Julien
> >> 


Casey Bralla
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