Home Networking with a One Way Cable Modem?

Blacklotuz asks: "I recently networked the computers in my house with a Linksys EtherFast Cable/DSL Router. Today I called up Comcast to order cable internet service, but because I live in a rural area we still have downstream only cable. I was told that in order to use the service I would have to connect the cable modem to the ethernet card on my computer as well as dialing up via the 56k modem. Im running Windows XP on the computer that will be dialing up. Does anyone know of a way to use a one way cable connection with a router?"

Just out of curiosity...

How much is ComCast charging you for such a brain-dead service?

And are you actually going to pay for it?

External modem a possibility?

When I had a similar one way service ages ago, I had a cable modem with a DB9 port for an external modem. Worked well, though I'm not sure what standard it used since it was wireless. You may want to check around for a different cable modem with this option.

more information

Does anyone know of a way to use a one way cable connection with a router?

A one-way cablemodem is a router. If you want to hook up another one, hook it up. Anything more requires you telling us why exactly you're trying to hook up a router in the first place.

One-way cable?

What is this, the dark ages?

Providers are starting to roll out DOCSIS 1.1 systems now, and DOCSIS 2.0 is only a few months out, if you believe CableLabs. Even so, most cable systems should be supporting high-bandwidth symmetric tiered service by next year.

Where exactly do you live?

with a router?

Why would you need a router? If you only have one machine, then you are set to go without a router.

If you have two machines, then you have two options as I see it. First (1) is to use the XP box to proxy the I-Net connection out to your other box, or (2) set a third computer up to do that for you. Any machine that has a routing table like the one that they are asking you to setup will be robust enough to handle any day-to-day routing that you might be talking about.

If that doesn't answer you question then, I guess you want a black box router that you can run through. All I can say is "My condolences to your dreams". After a cursory look over the web I have found plenty of routers with Ethernet/serial ports, but the thing is they use them as separate ports, and you want to use them as a MUX of sorts. If you got a cisco2500 (?) then you might be able to route all outbound traffic to one side of the box, and allow inbound traffic to run in from anywhere.

I'm not so sure that this would allow you to make and maintain a connection to your dialup ISP, but it may make your dreams come true. Also note that compared to my earlier solution, this one would be VERY VERY expensive.

This isn't that hard

Plug the Linksys into the cable modem. Plug the computer into the Linksys. Plug the phone line into your computer. The Linksys should be transparent to you. It should be opaque to the rest of the world.

More Info

I have the same situation setup right now through RCN. I likewise live in a back-asswards area with only one-way service. The cable modem connects directly to the modem through a standard modem cable. The cable modem than plugs into the Linksys router which plugs into the hub.

use linux bonding to solve this?

you might be able to use a linux server to do this. i'm not sure if it would work, but here's the idea:

1. you'd need a linux machine, phone modem, and 2 ethernet cards (one for the cable modem, one for the router).
2. use the linux bonding driver (multilink) to combine the phone modem interface and cable modem (ethernet) interface.
3. set up ipchains or netfilter to make all traffic go through the bonded interface to the router interface and vice versa, preventing any from reaching the linux machine itself (you want the linux machine to be transparent).
   
   that should give you the single bi-directional interface to plug into your router. you might also try
   
   
4. running it as a halted firewall [samag.com] for a bit of added security.

i don't know enough about bonding to say whether this would work or not, can anyone help me out here?

rural cable?

Not to be a troll, but I think you should consider yourself to be lucky to receive cable television at all in a rural area. I live just two miles outside of a town of about 500, yet I do not have access to public water, waste, garbage, gas, or cable services. My electricity comes from a rural co-op, which thankfully, is quite cheap. Telephone is similar, though my local calling area is worthless... about the only folks I can call local is a town of about 250 that's about 20 miles to the east of me. I can't even call the nearby town nor the nearby city locally.

But that's about the end of my rant. I wouldn't give it up for anything. The trees, the quiet, the river, the lake. "We're from the country and we like it that way". And because of my consulting business I can afford a T1 from Sprintlink.

what about the simple route?

Why not simply set up one of your machines as the router. Hook the internet into it. THen hook that into your network, since I assume right now your only using the switch part of the linksys box anyway. THis will turn the main machine into a router. If you want to be able to dial out from any machine in the network, you could use something like VNC or pcanywhere. You can then sell the linksys box and just get a switch, using the money for other things. Windows XP makes all of the networking INSANLY easy. Just run Network Setup Wizard.

What's with one-way cable ?

Why does distance have anything to do with it ? If you can receive data one way, then why can't you send data the other way ? The physical link is there, it might be a little laggy compared to a downtown setup but should still work, no ? Especially since cable uploads are always capped at a fraction of the downstream, things should work just fine, but without hogging a phone line.

Cable bound to a 56k really defeats the purpose, since a big selling point of cable is that it's "always on", just fire up a browser and let it rip. If you have to go back to the dark ages of phone dialing, then it ain't worth squat. Get ISDN instead.

Not possible

It is not possible to have a linksys router do NAT on a downstream only connection. Why? - The way NAT works is (partially) by identifying outgoing sockets. Without this, NAT is useless. On the other hand, you could use proxies however.

To use NAT though, both the upstream and the downstream must be connected to the same routing device. An old computer would do the job nicely.

Motorola SurfBoard Modem

A good friend of mine had the very same situation, upstream-only cable modem. The cable modem that he was provided with, however, did the dialing, NOT his PC. He instantly was able to use a broadband (LinkSys actually) router. Look into that possibility.

You need a "telco-return" cable modem

Motorola and 3com both sell cable modems specifically engineered for your situation. Sell or return your existing box and buy one. Your TV cable and the modem link will plug into one box, which will in turn connect via ethernet to a single PC, or to a cheap ethernet hub (or switch) which can then be connected to multiple PCs.

If you'd rather do it the hard way, get an old PC from the recycling bin (or some corporate dumpster) and run linux/IPtables or OpenBSD/packetfilter and use gated to manage the routing. The PC will be your router/firewall.

If you choose the second option, you are going to retain the linksys, so be sure to get the latest firmware download for it because those things are notoriously crackable. If you choose the first, be careful with the ethernet side of the cabling - you will need a different cable (a crossover or hub-to-hub cable) from a cable modemhub or switch than you would from the cable modemPC.

I've done this before

It's not hard. First challange is to get your happy little linux box using the cable modem on its own. The problem is that some distributions (and most sets of firewall rules) disable having a request go out one interface and the reply come back on another. There's a setting somehwhere under /proc to allow that traffic, but I don't have access to my boxen right now so I can't look it up.

What the cable company is doing is assigning you a static dialup address and then associating that address with the cable modem's MAC. This allows you to call out, but inbound traffic is routed to your cable modem. As far as the internet is concerned, your IP address is the one on your PPP interface.

Once all that is working, standard NAT implementations should work fine. The IP-Masquerade HOWTO is a fine place to start. Keeping in mind that your external interface is your PPP adapter, NOT the ethernet to the cable modem.

This sort of thing may or may not work with Windows intert connection sharing.

Ugh.

1-way cable? Forgivable.
Dumb questions about routing? Everyone has to learn at least once. Forgivable.

Using a linksys router? Retarded.

Seriously, short of buying a catalyst 5000, nothing beats a linux (or BSD, I suppose) box. Got that old weird vintage computer with only an arcnet nic? A linux router/firewall will put that on the net too. 1 way cable modem? Linux supports modems and ethernet. Want to do something fancy? Linux can do almost all of it. Firewall rules need to be a bit more complex (which yours will be) ? It can do that too.

A linksys costs money better spent buying some 10/100 nics, a switch, junk food, hookers... nearly anything, you name it. It can't do a single thing I've listed above. Some things are beyond your control (being stuck in the boondocks), but others are flat-out, no excuses possible, mistakes. Correct them quickly, and then return for some useful answers...

The cable modem already does that...

It's quite easy: the cablemodem has a serial port that is connected to the modem, and is programmed to dialin whenever it has upstream traffic. From there on, it's all ethernet, baby :-)
So you're free to use any router you want.