HOW TO: Building an Out-of-Band Device…

HOW TO: Building an Out-of-Band Device…

Oob Cross SectionHere’s a great article from Tom Bridge on building an out-of-band device: “When Hurricane Katrina ravaged the southeastern United States in late August 2005, telecommunications networks were interrupted in a significant fashion as switching facilities were flooded and power disrupted for days on end. Our Jackson, Mississippi office was left without a T1 when power was restored, as the route for our MCI/UUNet T1 travelled first through New Orleans. Facing days or weeks of a dark T1 was more than our company could take, so we decided to build them a fully functional dialup router using a spare 56k modem from our old dialup bank, a dialup account with a national provider, and a Netgear wireless firewall.”…The Parts We Used:

  • US Robotics v.Anything Courier 56k Modem (Free, from the scrap heap)
  • Netgear ProSafe Wireless Firewall (FWG114P) ($158)
  • 25pin to 9pin serial cable ($3)
  • Cable ties (zipties) ($5 at the hardware store)
  • An Earthlink account ($20/mo)

The basic philosophy by this device is that it acts not just as a dialup router, but as a DHCP server for your local network on the same subnet your network would ordinarily be using in full operation. Our office is using a Cisco VPN to provide secure communications between our locations, and as such, each of our locations has its own 10.10 Class C ( – is our “home” subnet). For our example here, we’ll be using 10.10.4.x as the IP range.

Oob Cross Section-1

Configuring everything is fairly simple, but does require an attention to detail. Unpack the Netgear firewall and set it up with a power connection. Using either the wireless connection it creates, or the ethernet hub on the device itself, open the admin interface located at The password and username are inscribed on the bottom of the firewall, and should be admin:password by default. Once in the administration interace, please change the password at a bare minimum to prevent undesired modifications to the configuration you’re about to create.

Oob Side

One of the reasons that we chose the Netgear device for this task is that it has a serial port for an external modem, the second reason is that it can use that modem as its primary internet connection and the third reason is that it can behave as a router on any configuration you choose to give it. This last part is crucial for us, as many of our office devices, including two printers, a copier and our other wireless hubs depend on fixed IP addresses that other such devices (Apple Airports in specific) will not honor.

The Oob

Once you setup a new username and password, and a new SSID for the network, it’s time to setup the internet-side TCP/IP configuration for the OOB device. This is where the Earthlink account comes in mighty handy. You could do it with any dialup number, but in such cases as this, where long distance telecommunications have been disrupted, it’s important to use a local number for dialing, as long distance circuits will be in high demand if they’re working at all. Earthlink maintains an up-to-date list of local access numbers at their website: and in our case there were four numbers for Jackson, MS. After cursory dial-in attempts from our location, it was easy to find which number was working the best. Adding the account information to the router, and the local seven digit dialup number, is fairly simply done from the administration interface. Set the dialup connection as the primary method of internet access (a radio button in the configuration) and then reboot the router.

Once the dialup connection is in place, it’s time to add the router-side TCP/IP configuration. This is just like setting up any other router, make sure to have the IP address for the router in place, as well as a valid subnet mask, and some DNS servers handy. Earthlink lists their DNS servers on their account page at: Once those are plugged in, set the DHCP range for the network config and get everything ready to go. Once this is done, apply the configuration and power off the wireless firewall.

Now it’s time to prettify the whole thing. Place the larger of the two boxes on a good workspace and attach two cable ties in series. Slide these underneath the larger of the two boxes. Now place the smaller box on top of the larger box and use the serial cable to connect the modem to the firewall. Looping the cable carefully, place the serial cable between the two boxes. Now loop the cable ties carefully over the top, placing the joint of each along one edge of the two devices for traction. Secure the cable ties, making sure not to place undue stress on either end of the serial cable, blocking an ethernet port, or causing the power cables to kink or be otherwise harmed.

Now, using a set of small cable ties, secure the two power cords together. Each device will likely use a wall-wart style transformer on the end, so be wary that you may need some slack at that end of the power cable. If you like, you can use a three outlet extention to make it so that the OOB device uses only one three-prong grounded outlet. I didn’t do this, simply because I had a budget of $200.

Once complete, setup and test the router, making sure that the modem is dialing and connecting, and that the router is giving out appropriate DHCP addresses and allowing for network access. Test both the wireless and the wired connections just to make sure you didn’t miss anything. Pack it up, and send it just ahead of any storm, or in response to any crisis. While 56k dialup won’t be good for surfing boingboing or watching streaming video, it will allow for data transfer including email, instant messaging and other low-bandwidth activity. Better still, it allows for one dialup account to serve an office of several people without taking up more than one phone line at a time.

These are great devices to have as spares, and can be assembled with very few parts, very cheaply in less than an hour’s time.

20 thoughts on “HOW TO: Building an Out-of-Band Device…

  1. vonSlatt says:

    Back in the last century we used to do the same thing, only all we had to work with were razor blades and a broken off piece of pencil stub . . .

    Seriously, last year we ran a company of 40 off of a Toshiba Satellite Pro (P-I 90 mhz) laptop with a 56K modem and Windows Internet Connection Sharing for two days while Verizon pumped all the water out of the manhole up the street. It worked surprisingly well!

    10 house point to whomever can tell me what one _would_ use a broken off pencil lead and a razor blade for? Hint: it has to be a truly old fashion blued carbon steel blade, not a stainless blade.


  2. tkarches says:

    As much as I like making stuff, an older Apple Airport works just as well for this purpose. I did this when our church lost its’ Nextel modem access and had to wait 3 weeks for RoadRunner. Once it was set up, I never had to mess with it. The office did web surfing and email. The email accounts were all IMAP, which helped mimimize bandwidth requirements.

    Get one of the platinum ones with the built in modem. Should be able to pick one up for less than $100 on eBay.


  3. ragaskar says:

    10 house point to whomever can tell me what one _would_ use a broken off pencil lead and a razor blade for? Hint: it has to be a truly old fashion blued carbon steel blade, not a stainless blade.

    Radio Receiver.

    That said, you have GOT to be kidding me. This is a make? The dude essentially used two components as they’re meant to be used.

    hangon, let me ziptie my wireless card to my laptop HOLY SHIT I BUILT A WIFI APPLIANCE THAT RUNS WINDOWS XP

  4. ScrappyLaptop says:

    Aw, vonSlatt, that’s an easy one: It’s a “foxhole radio” circa WWI! But, I made ’em as a kid out of a safety pin, orange juice can, thumbtacks, a block of wood, some doorbell wire and the aforementioned blued razorblade. The only part I didn’t make was the $0.99 white earphone.

    Funny, I’ve used a Satellite Pro (440cdt, so it was a P120, I think) as a dialup router, too, but I ran Freesco. So, really, if you have a spare laptop with a built in hardware modem lying around, you could meet the goal of this entire article just by keeping a single 3-1/2″ Freesco floppy disk in your desk drawer! When the emergency is over, pop out the disk, reboot and your laptop can resume it’s prior role.

  5. jcantara says:

    Pete and Repete went into a building, Pete came out, who was left? No seriously:
    And it’s still just as lame as when I originally commented on it.

  6. vonSlatt says:

    10 points to both ScrappyLaptop and ragaskar for the correct answer with 5 additional points to ScrappyLaptop for the “foxhole” part which is what I was thinking.

    You guys must both be as old as me! – actually I was never able to FIND a blued carbon steel razor blade so maybe you guys are just a little bit older! ;-)

    My Crazy Projects

  7. vonSlatt says:

    Grr . . . I keep forgetting the “”s in the href tag.

    My Crazy Projects

  8. vonSlatt says:

    Here’s an article about foxhole radios.

    Back to the subject at hand; Windows Internet Connection sharing is trivial to setup and almost everyone already has it – but I’d use OpenBSD if I were going to build something to keep on the shelf for an emergency.

    My Crazy Projects

  9. cajun says:


    A pencil lead and razor blade can be used to make a radio detector. Just add a set of headphones and, “voila”, you can hear a strong AM radio station in your area. A better choice for the pencil lead is an old fashioned (all netal) diaper safety pin).


  10. cajun says:


    A pencil lead and razor blade can be used to make a radio detector. Just add a set of headphones and, “voila”, you can hear a strong AM radio station in your area. A better choice for the pencil lead is an old fashioned (all netal) diaper safety pin.


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