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Home Networking with a One Way Cable Modem? 54

Posted by Cliff from the routing-around-the-problem dept.
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?"
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Home Networking with a One Way Cable Modem? More

Home Networking with a One Way Cable Modem?

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

    And are you actually going to pay for it?
  • 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.

  • 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.

    • Re:more information (Score:2, Informative)

      by fist_187 ( 556448 )
      a cable modem is a bridge, not a router. unless it has 4 ethernet ports and says "router" on it, a cable modem bridges DOCSIS protocol to ethernet protocol.

      a router doing IP masqerading (the linksys in this case) needs to know the outgoing data so it can correctly route the incoming data. so, you can't hook the router up between the computer and the modem and expect it to work.
  • 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?

    • Um... not a troll... I'm serious.

      I know that there are still some areas where two-way cable is not available, but that's the provider's problem, not yours. If you want broadband, don't give money to a provider for shoddy service -- go with a viable alternative.

      I would say that if you don't have good cable (the system you're talking about is several years obsolete -- read the parent comment), you probably don't have good phone lines either. Your bottleneck will be the upstream connection, not your routing configuration on your end.

      As the AC above me said, why not try full-duplex satellite? I doubt the latency will be much worse than going up the POTS and back down the cable. And these days, the price isn't significantly more either.

      The long and the short of it: this is like taking a Model A out for a spin and then wondering why people keep honking at you on the highway. Sure, it's better than walking... just not very much.

      • "As the AC above me said, why not try full-duplex satellite? I doubt the latency will be much worse than going up the POTS and back down the cable. And these days, the price isn't significantly more either."

        Umm, not quite. My 1 way wireless cable has ping times around 100-200 on average, and the Starband I tried always had a minimum of 600 or so. Big difference, as one is still usable in games, the other one isn't.

    • I currently reside in Eastern PA and it is the dark ages here. The cable here is awful, they say they offer one-way cable, but the signal here is so bad that I doubt any decent speeds could be attained. The bunch of morons known as Service Electric [sectv.com] are the provider for our area. They're one of the of the oldest cable TV providers (which leads me to believe that they've never updated their equipement and the original cable from over fifty years ago is what their network is based on). They say they have the most advanced telecommunications and online services available but don't let that fool you. They only thing they've done that is anywhere near advanced is that you can now you can pay your bill online for their lousy signal and even worse channel selection.

      We can't get DSL because of the greedy fucking bastards who could give a shit about their customers and just barely pass as a legitamate company called Verizon [verizon.com]. On an additional note, GTE^h^h^hVerizon hasn't updated the equipment in our area for so long that they actually ran out of phones lines on the trunks that service our neighborhood.

      The real reason T. Ridge became the Director of Homeland Security was to get his ass out of this lousy state. Thankfully, I'll have job soon and I'll also be leaving this god-forsaken place behind. But I'm not bitter at all...

  • with a router? (Score:5, Informative)

    by tenman ( 247215 ) <`moc.iausten' `ta' `gro.todhsals'> on Wednesday May 29, 2002 @01:17PM (#3602888) Journal
    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.
    • Why would you need a router?

      Erm, uh, perhaps because s/he wants to take advantage of a firewall (built-in to many consumer routers) on the outbound link, lest any nasty packets come back upstream? Of course, if s/he trusts the cable company, this is moot.

      Then again, there may be the simple desire to eventually NAT several PCs, though having the inbound and outbound traffic split might make this difficult.

      • Erm, uh, perhaps because s/he wants to take advantage of a firewall

        What would prevent this from being done using my solution? Most proxy (internet sharing) softwares comes with some form of protection, and what the packages doesn't come with it is easy enough to download a free firewall that will work WITH the proxy.

        there may be the simple desire to eventually NAT several PCs

        I assume that when s/he says "Im running Windows XP on the computer that will be dialing up" that means (1)there is another machine that will not be dialing up, and (2) that there will be another machine(s) that need to use the connection.

        If I'm wrong, then... well, nevermind there is no way I'm wrong :P

        BTW: I still haven't found a solutions to the problem.
        • Erm, uh, perhaps because s/he wants to take advantage of a firewall

          >What would prevent this from being done using my solution? Most proxy (internet sharing) softwares comes with some form of protection, and what the packages doesn't come with it is easy enough to download a free firewall that will work WITH the proxy.

          Perhaps you trust non-dedicated firewalls (i.e. in the networking stack of the user's PC), but I prefer a dedicated machine for this.

          Finally, I don't like the idea of being dependent on a user PC to mediate my network connection -- if the other PC crashes, or becomes busy with someone else's work, my network connection suffers. Of course, as a "poor-man's" approach, it's quite workable.

          • before I reply, what is the mood of your post? are you trying to be better-then-thou, and a network security zelot? or are you just trying very poorly to get me to see your point?

            Please reply with haist to I know how to respond to this garble.
            • I am not trying to come off as "better than thou", by considering a dedicated firewall/router better than relying on each (or only) user PC to act as a firewall. Economics may dictate that such an external firewall may be unaffordable, but only you can decide what the security of your system is worth.

              As for being a network security zealot, I would consider that "stronger security is better" and evaluate security measures on a "security vs. convenience" and "bang for buck" basis. An external firewall/router is not inconvenient, and provides good value (around US$200). I don't go so far as to use encrypted filesystems, though I have considered it.

              Finally, the use of a dedicated firewall/router is commonly advocated: I am not alone in this view. In fact, when I got my always-on line, my ISP very strongly reccommended I get one -- the idea being that if I could afford $80/month for a DSL line (I'm so far from the CO that I had to spring for a dedicated dry pair at $15/month), I could certainly afford a $200 firewall/router.

              In the scenario presented, securing traffic on the outbound channel may not be possible, without some effort (I envision a dedicated PC acting as a router AND a telephone switch for the modem line -- you could NAT this way too), and SOME firewall is better than none, but I can't help think that any ISP that prevents the use of off-the-shelf solutions for common security problems isn't worth dealing with.

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

      Well, if you read the first sentence of the post,

      "I recently networked the computer
      s in my house with a Linksys EtherFast Cable/DSL Router.
      The "If you only have one machine" proposition is provably false. There is more than one computer, so a hub/router is already there.
      ______

      That having been said, if the Linksys router can't handle split cable/phone routing (this is an RTFM question), then you may need to use a solution like a dedicated linux/bsd box in front of the router. It doesn't take much. An old P/166 w/ 32M of ram and an 800 MB hard disk is plenty. We used to use 386/25s to handle 10Mb ethernet traffic at the Department of Computer Science (but they didn't do any serious firewalling, that I know of). Using a box 6 times as fast to handle 1/10 the traffic bandwidth should be pretty easy.

      • Linux on one-way? sorry, try again.

        the system for this is unbelievably braindead, so it only works with special software in MacOS and/or with the broken TCP/IP in windows (They do the bonding by just setting the correct src ip in the 10baseT traffic coming from the cable modem...)

        just set up ICS on the XP machine (despite what the cable company says, this should work. the modem doesn't set the dest right.. and windows doesn't really care).

        put the router off of there, and then run your machines behind that, if you really care to.
        • just set up ICS on the XP machine ..... put the router off of there, and then run your machines behind that, if you really care to.

          If it't that horribly bad, then I might not do it at all... There's no way that I'm gonna put a Microsoft Windows box in on a cable modem with no protection. It'd be like wild unsafe sex at an AIDS hospice: In a week, or two, you'd have every virus in the book.

          • I was just looking at a solution to protect an XP box from doing anything I didn't know about (inbound and outbound) and came across ZoneAlarm, apparently a very capable protection system for Windows. They have a free version as well as a 'Pro' version. Checkout www.zonealarm.com.
          • eh, i had no problems with it. i also don't use IRC and i didn't run any public servers (for the obvious reasons that connectivity sucked. and that it went down 3-4 days a month...)

            any of the boonie-broadband alternatives require use of MS windows, sadly. just lock the machine down, and go from there. i ran _zero_ public services from the machine, and didn't ever use it to do anything (the occasionally foray into IE5 excepted... it was my only windows machine).

            just get a decent portscanner and scan the machine regularly, noting any changes. should be plenty of self-defense.

            if i had stayed in my previous house any longer i might have some progress on the linux bonding front, but i didn't, sorry. currently living off "borrowed" cable from my neighbor and then going to europe in a few days =)

  • This isn't that hard (Score:2, Informative)

    by PD ( 9577 )
    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.

    • Seems to me that it won't work because the Linksys router is putting his computer in a NAT'd network. Since the outgoing traffic is going through the modem instead of the Linksys the IP stack on the Linksys won't know what outgoing connections are open, and so it won't be able to route incoming traffic to the appropriate computer.

      I could be completely wrong, though. That's for the mods to decide.

  • More Info (Score:3, Informative)

    by bassburner ( 574908 ) on Wednesday May 29, 2002 @01:18PM (#3602897)
    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.

  • 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?

    • Well, you have an interesting idea. The bonding idea is BS, though.. I'm not sure what you were thinking :)

      But, as you say, if you simply route (routing should work, you shouldn't need NAT) the packets from the router to the modem interface, it should work well enough. Unfortunately, once you get a dedicated box to do this, you might as well use IT as the router, unless you have a special reason :)

      • bonding and NAT both don't work. Trust me, i tried. i should still have the scripts that i played with (hell, i even tried kludging the bonding driver to allow ppp/eth bonding)

        i have yet to see anyone actually accomplish this on linux.

        your best bet is to take a little POS 2k or XP machine and run ICS on that. if this is all you runo n that machine, it should be plenty stable.
  • 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.
  • 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.

    • Re:what about the simple route? (Score:1, Funny)

      by Anonymous Coward
      I don't think he can do that, the internet is already hooked to my computer and I'm not done with it.

      • Re:what about the simple route? (Score:1, Funny)

        by Anonymous Coward
        So, you're the bastard that's holding thing up. I wanted to download the internet onto my computer last night but the internet was down.
  • 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 so much as distance, but customer density. Putting in a neighborhood upstream station isn't cost effective if only a few people are using it.
    • Cable is designed for one-way traffic to begin with. When people started wanting data over cable, a beast called "return path signal" was introduced. This is how the upstream connection works. Old cable equipment doesn't *easily* let this signal get back to the equipment that needs to receive it, from the cable modem in your house. It doesn't actively do anything to *block* it, per se, but it doesn't make it easy. Sometimes, this can be overcome with a return-path amplifier (as in my case), but sometimes, there just won't be enough signal either way. The downstream signal will *always* be stronger, because that's what the cable system was designed for to begin with. Now, I'm no cable expert, so don't flame me, please. This is just what I've picked up from the various technicians that have come through my place, telling me that the splitters used in my apt. complex are OLD and don't let a certain signal range through cleanly, as they should. As I said before, a return path amp fixed me right up. But, I don't live out in the boondocks, so for me, it was mainly getting the signal strong enough so that it got past the various splitters installed in my building - once it hit the node, it was golden from there on out.
      • Ahh.. well then that's the golden difference : up here, I wouldn't trust the cable tech with a screwdriver, I'd much less believe whatever he tries to tell me. That scepticism of mine started wayyy back in 1998 when I recognized the cable installation guy : he was a former Bell ISP tech support agent, back when I was working there too. Nevermind the fact that he was an IDIOT agent, who would just waste the client's time and let the next guy fix it. Anyways, up here in Canada we have a serious shortage of expert people in all fields, so most 'experts' are just college students with a fancy nametag.

        "- I've been IP-less for the last two hours. What gives ?

        - Please reboot Windows and try again.

        - This is a linux system, and I've already checked my end. Is the DHCP server down again ?

        - We don't support linux. Please install Windows and call us back. "

        Needless to say, I called a few marketroids and weaseled out a free month of service :) Still it goes to show that big cable providers suck because they hire minimum-wage clowns that still wear velcro sneakers.

  • Not possible (Score:2, Informative)

    by EdMcMan ( 70171 )
    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.

  • 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.
  • 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.

  • 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.
  • 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...
    • Read the other posts on this story - nobody's gotten ethernet + ppp to work via a Linux box, so in that case, no, a Linux boxen wouldn't work for this guy. The best (and simplest) I've heard so far has been getting a cable modem that handles the POTS modem itself, so that the router (be it consumer ware or a Linux boxen) can connect to the cable modem (only) and not have to worry about where the packets are coming from and where they're going!
      • I'm struggling to remain civil here.

        No one that we know of, has gotten this to work, it's true. Or rather, they haven't specifically gotten it to work with a 1way cable modem and 56k. However, many have gotten *very* similar setups working using any number of different interfaces.

        So, the contention that linux isn't suitable for this borders on the inane. If he wants to do nice and/or cool things, he'll have to be willing to be the first, sometimes.
  • 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.

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