Linux Token Ring Support Bringing Down Corporate Nets?

mjh asks: "I've been running Debian GNU/Linux on my company supplied laptop for 3 months now. I got permission from my manager to run it on the network, but I did not go through the somewhat rigorous process of getting the software certified. I have legitimate business reasons for using it on the corporate network (which is why my manager approved it). I even managed to get Lotus Notes to run under wine so I never had to boot into Winders at all (unless someone sent me a PPT doc). I was pretty happy...until I brought the entire network down." Anyone else running Linux on a Token Ring network who would care to talk about their own experiences?

"My company runs Token Ring at the office (puke!) I got drivers from the card manufacturer (Madge), and I'd been happily churning along. Then last week, we started seeing a bunch of errors on the network. These errors would bring everyone on the ring down. After a week of this kinda stuff, they eventually isolated it to me.

Reboot the laptop into Windows and the network card works just fine and they don't see any ring errors. Reboot into linux, and suddenly they start seeing ring errors. I don't really grok token ring, so I'm not entirely certain that I know exactly what the problem is. But, whenever I brought the token ring on line under linux, they saw ring errors, which eventually (as I understand it) would bring down the entire ring. Switch cards (same model) and it continues to happen. It looked to me (and the network analysts) that the Linux driver was causing the problem.

I tried switching to an IBM token ring card, but there's a bug and I hadn't patched for this. The people with the fluke would not wait around while I tried to figure this out. I didn't have any other token ring cards that I could try.

In the end, I agreed not to boot into Linux unless I went into the conference room (which is one of the only rooms in the building with ethernet ports). How should I have done this differently so that using Linux would have been a more positive experience for my company?"

Comments

Re:Voodoo debugging

[mjh]

A "receiver congestion" error is caused when the Linux driver doesn't remove packets from the card's buffers fast enough. In theory, they are suppose to indicate that packets are coming in too fast for the machine to handle. In practice, you see this happen when machines "hang" and fail to empty their queues. You might be running some sort of libpcap packet-sniffer on the system or have the adapter running in promiscuous mode (do an ifconfig to check) that is having some sort of pathelogical condition.

Wow! This has *got* to be what the problem was. This problem started showing up right around the time of the big Code Red hubub. So I installed snort just to watch and see what was going on. Snort, of course, uses libpcap and puts the card into promiscuous mode. Right afterwards, is when we started seeing problems on the network.

My guess is that your admins are just getting testy over the fact that your Linux box re-inserts itself more often than Windows boxen, causing a higher number of relatively harmless burst-errors. When they diagnose problems with the ring, they notice that your machine causes the highest number of errors, and therefore blamr any ring failure on you.

Holy schnikies! You must have been in the room! That is *exactly* what happened. They discovered these errors and basically said that the errors were the *only* thing that they could see that was wrong with the network. From this they concluded that the problem must have been caused by my running Linux.

About the only thing that does not fit, is that since I've stopped running Linux on the network at work, the problem has completely gone away. Not a single recurrance in several weeks time (I actually submitted this article to /. many weeks ago. Why it took so long to get accepted, I dunno.) They did, as part of their process of troubleshooting replace all of the TR equipment in the closet. But even after they did that, we were still having problems. So far the only thing that seems to have fixed this problem was me staying out of Linux.

Thanks for you're very informative post!