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Bridge Ethernets Over T1?

Posted by Cliff on from the time-saving-networking-hacks dept.

michael_cain asks: "I have to take a series of demos 'on the road' occasionally and have to have a data connection back to the home lab. In many cases this takes the form of a T1. In order to terminate that at both ends, I currently have to have a CSU/DSU and baby router at each end. I would like to simplify this arrangement; does anyone know of a pair of small boxes that would let me use a T1 as a simple Ethernet bridge (well, a learning bridge would be nice)? Just plug the T1 into one side of each, a 10BaseT or 100BaseT into the other side of each, and relay Ethernet frames back and forth?"

9 comments

  1. Nice idea by bencc99 · · Score: 1

    I don't know of any offhand, but it could be very useful for the rest of us as broadband becomes more common...

    1. Re:Nice idea by bencc99 · · Score: 2

      Sorry to reply to my own post, but as a second thought, try FreeSCO which is a free linux based router - it probably isn't quite as compact as you're looking for, but runs nicely on modest hardware, and couldn't be easier to set up. A couple of low end pentiums with a pair of net cards in slimline cases would probably do the job nicely.

  2. A Bridge Too Far by Anonymous Coward · · Score: 2

    Deep in the bowels of the Ethernet spec is a maximum propogation delay between hosts. This limits the distance between hosts. I don't recall the exact number of milliseconds, but I think you're limited to about a campus size. Perhaps a smart bridge could get around this by buffering. If you just want to reduce the amount of equipment you lug around, try finding a high speed serial port that will handle T1 for one of your computers and run PPP, that will eliminate the seperate router or bridge. (Assumes an OS that will route IP.) We use an SBus card from Sun to do this, and I think we've considered PCI versions.

    1. Re:A Bridge Too Far by michael_cain · · Score: 1

      Yes, I was assuming that the box would be buffering frames. I don't recall the allowed propogation delay in milliseconds either, but the total length of a coax Ethernet is limited to about a kilometer. I think there's also a minimum spacing restriction as well, coax taps have to be at least two meters apart?

  3. LRP and Sangoma WAN-PIPE by Anonymous Coward · · Score: 1

    THere are a few ways to do this... A small footprint PC, combined with LRP Linux a single floppy based distro, and a Sangoma WANPIPE and poof T1/Frac T1 Router/Bridge w/ integral CSU/DSU. With the cost of Pentium and older 486 computers these days this makes a good combo.

  4. Eliminate/Integrate the CSU. by gillham · · Score: 3

    A baby router with an integrated CSU/DSU is probably what you want. Then you have the option of routing IP or bridging traffic. (depending on the router you buy) It could also act as a DHCP server, NAT box, etc which might be useful.
    A cisco 1720 with integrated CSU/DSU is about $2200 list price.
    Or, buy a synchronous PCI card with integrated CSU/DSU (~$600) and install it in your demo server.
    If you're just using a laptop, perhaps one of the docking stations with a PCI slot would be workable. Dell has these.
    This would require drivers under your OS, etc so it would probably be more of a hassle than just integrating the CSU/DSU into the router. Also with the router you can hook anything to it, and you don't have to worry about having drivers, etc for your OS.

  5. Yes you can do that with OpenBSD by bumbaclaat · · Score: 1

    you just use PCI T1 interface cards, and regular
    ethernet cards.. As a plus, you use IPsec to encrypt the traffic. You run the OpenBSD bridging to bridge together the two networks.

  6. Cheap, no, easy, yes. by Above · · Score: 1

    Any old Cisco IOS based box will do the trick. Start with this link to get basic transparent bridging information.

    If you look further down, you'll see "Ethernet Bridging Example" with Figure 40 in it, where they route IP and DECNet, and bridge everything else. Well, if you remove IP and DECNet, it works too.

    Of course, the request was for a cheap box. IOS based boxes are far from the cheapest, particularly on the low end. A 1605 would be about the cheapest thing for the job. Most any "router" on the low end that also supports bridging will do the job, bridging over a WAN is pretty easy.

    That said, why not just route?

  7. VPN by macdaddy · · Score: 1
    Two simple linux boxes and VPNd!