[lug] cable modem network topology

D. Stimits stimits at idcomm.com
Sat Jul 20 23:45:08 MDT 2002

Barney Treadway wrote:
> FWIW...
> Our office runs on a single cable connect coming in through a RCA cable
> modem that drops into a cheapie Lynksys router (<$100). Macs, Linux, M$ all
> live happily behind it. The little config tool for the Linksys is very easy,
> open ports where you want em, set up the dhcp etc however you want. Can even
> get the wireless + 4 port for about $130 or so.

I am avoiding wireless, I don't like the security, and probably even 
worse, latency. I already have a good 8 port switch and several network 
cards, even some Fast Cat 5 cable (though probably not enough). However, 
the idea of a single unit that routes for multiple DHCP clients does 
intrigue me. My question is whether it does this through some form of 
proxy/NAT/masquerade, or if it leaves all units fully visible on all 
ports (desired for a few quirky apps that need the outside to come in 
for contact)? Is it possible to add a Linux firewall in there with this, 
even with something like 3 DHCP machines acting independently (which is 
why the bridging filter has been a hot topic for me)? If this thing is 
configurable for firewalling, and does all the DHCP bridging/routing, it 
just might be a good idea.

D. Stimits, stimits @ idcomm.com

> With the "always on" we never lose our IP, except when they lose it for us.
> B
> ----- Original Message -----
> From: "D. Stimits" <stimits at idcomm.com>
> To: <lug at lug.boulder.co.us>
> Sent: Saturday, July 20, 2002 3:46 PM
> Subject: Re: [lug] cable modem network topology
>>Terry Branaman wrote:
>>>On Fri, 2002-07-19 at 18:23, D. Stimits wrote:
>>>>That reminds me, does anyone know if the AT&T cable comes with choices
>>>>on cable modems? If so, are there good/bad choices here? I assume
>>>>external is best, but I read in one FAQ already that at least one cable
>>>>modem is PNP set to require the o/s be PNP-aware. Now if the modem is
>>>>rented ($2/month), I wonder how they feel about running a utility to set
>>>>it to non-PNP-aware.
>>>When I signed up, the rent was more like $10/month or higher, so I went
>>>out and bought a Toshiba cable modem. I just looked for a modem that has
>>>the certification that they require (as listed on their web site). It is
>>>external, and has a 10-base T port, so it plugs in to the NIC in my
>>>firewall machine, which is using Linux. I just had to set up networking
>>>to use their DHCP server, since they won't assign static IP addresses.
>>I'm looking more closely at their advertisements, and comparing to what
>>the guy told me on the phone. It looks like you are right about this,
>>and maybe it is even as high as $15/month charge. There is mention that
>>you are allowed to purchase your modem either directly from AT&T, or
>>else buy it elsewhere. I am thinking of looking around to see what
>>stores have, if any are available. Do any of the local retail stores
>>actually sell cable modems? I would think it is a product available only
>>online, but I kind of wanted to look at the boxes. I don't imagine many
>>people in Boulder use cable modems, since DSL is so popular there. But
>>by the time you include the cost of the phone line itself, the cable
>>modem seems far cheaper. I am beginning to like the idea of a bridge (or
>>backup idea from Sean, proxy ARP) on cable modem better and better (to
>>tell the truth, I kind of have fun setting up this sort of thing, so
>>long as there is no schedule that says I have to work 24/7 to meet a
>>deadline). My guess for local retailers that sell cable modems would be
>>CompUSA, but almost nobody else (Circuit City?). I will shop online, but
>>if anyone knows of stores that have such products in stock where I can
>>walk in and look at the box, give me a shout.

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