A semi-easy firewall

A single-floppy firewall mini-distribution can be a quick and easy way to save yourself some money if you’ve got an old PC in a closet not doing anything, assuming you stumble across a combination of hardware that works right.
If you don’t stumble across a combination of hardware that works together, you can just as easily spend a weekend and accomplish nothing but uttering strings of four-letter words in combinations never before heard by mankind.

In case you came here looking for hardware that works, here are a few hints. A 10-megabit PCI NE2000 clone in combination with virtually any 10/100 PCI card ought to work fabulously. A pair of 10/100 PCI cards based on the RealTek 8139 chipset, which includes the majority of today’s inexpensive cards, probably will not. If you’re buying new stuff and want ease of use, get a 3Com card and a cheapie. If you want cheap and a little inconvenience, get a Netgear FA311 or 312 and a Realtek 8139-based card, such as a D-Link DFE-530+ or a Linksys. You’ll have to hunt down and install the natsemi.o module to get the Netgear working; most other inexpensive cards on the market will work with the rtl8139.o driver.

Freesco doesn’t supply a driver for the Intel EtherExpress Pro series out of the box. If you’ve got an EEpro, you can make it work by downloading the module and copying it to the floppy, but don’t rush out to buy one. And yes, the 3Com and Intel chipsets are high-performance chipsets, especially compared to the 8139, but remember, routers are machines that pull packets out of a 1.5-megabit pipe (if you’re lucky) and shove packets down an even smaller pipe. In this application, a $40 big-brand card doesn’t give you any advantage over a no-name card that costs $6 at Newegg.com

While these firewalls will technically work fine even on a 386sx/16, trying to make them work with ISA cards can be a long, difficult road. Used Pentium-75s are dirt cheap (and Pentium-60s and 66s are even cheaper, when you can find them) and they’re a lot less trouble because PCI cards don’t require you to rejumper them or hunt down a plug-and-play configuration disk to find out its IRQ and address. I’ve had the best luck with Pentiums that used an Intel Triton chipset or newer (the 430FX, HX, VX, or TX). I’ve tried a couple of boards that had a SiS chipset of 1995 vintage or so, and I could get one network card or the other working, but not both. I don’t want to generalize and say that based on two isolated incidents that all Taiwanese chipsets are junk for this application–for all I know, the problem could have been the BIOS on those boards–but I’ve done this on a handful of Triton-series boards and done well on all of them, and on two SiS boards and failed. Your mileage will probably vary.

How much memory do you need? 16 megs is sheer luxury.

Once you put all this together, the question becomes whether you use a floppy distribution or a full-blown distribution. If you want peace and quiet and cheap, the answer is pretty easy–use a floppy and pull out whatever hard drive was in there.

A full-out distribution like Red Hat or Debian will give you more versatility. You can run meaningful Web and FTP servers if you want (and your ISP allows it). You can run a caching nameserver to speed up your Web browsing. If you feel adventurous, you can even install the Squid caching proxy and speed up your browsing even more (but either use a SCSI drive or put in a bunch of extra memory and run Squid’s cache out of a ramdisk–Squid’s performance on IDE is, to put it mildly, terrible).

I’m having a hard time finding the documentation on how to set up a second network interface quickly. I believe it involves the file /etc/interfaces and the files /etc/sysconfig/ifconfig.eth0 and .eth1, but I don’t have a Linux box handy to investigate at the moment.

Anyway, I like Debian for this application (of course) because I can easily fit a minimal Debian on a 100-meg hard drive.

Once you get your network cards all working and talking to each other, you can build your firewall using this online tool. I just copy it, then Telnet into my Linux box using PuTTY, fire up a text editor, and right-click in the window to paste.

If you want versatility and quiet and don’t mind spending some cash, pick up a CompactFlash-to-IDE adapter and a CompactFlash card of suitable size. Don’t create a swapfile on the CF card–you’ll quickly burn it up that way. Your system will recognize it as a small IDE drive, giving you silent and reliable solid-state storage on the cheap.

3 thoughts on “A semi-easy firewall

  • October 21, 2002 at 11:35 am
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    Also see http://www.coyotelinux.com for another good Linux-floppy firewall, the one that I use. Sold my old SMC hardware router on Ebay after I built this cheap FW.

  • July 29, 2003 at 4:47 pm
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    I am currently installing Debain via boot floppy to ftp. I need to find the natsemi.o module for the NetGear FA311 10/100 PCI Card. Any ideas as to where I can go to find it. And after I get it, and put it on a floppy how do I get it in the list of possible modules to install? Thanks for your help.

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