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Routers and switches and hubs, oh my!


Some material is very old and may be incorrect today

© September 2005 Tony Lawrence
September 2005

I bet you hear this as often as I do: "So I need to put a little hub over there to fan out the network?". I know they probably can't buy a hub nowadays anyway, but I still feel like I need to correct them: "No, you need a little switch".

There's a difference, of course. A hub is a bus, where every packet goes to every port. With a switch, only broadcast packets go to every port, and with a managed switch, even that's not necessarily true because you can control what goes where.

But as I said, if they pop down to Radio Shack or Staples or CompUsa, they are only going to find switches, so I could probably save my breath and safely nod agreement. You never know, though: the other day I had a call from someone asking if they should plug their cable modem router into an uplink port or a regular port. I of course asked what on earth he was doing with something old enough to even have an uplink port, and was told "it was free", which is a pretty good answer, I guess.

What has bitten me now and then is stray routers employed as switches. At one customer, I've been bitten three times by the same old router. I took the darn thing out of service years ago and replaced it with something better, but told the IT guy to keep it because, what the heck, it's a quick swap-in spare if his current router were to fail. It wasn't too surprising to me when that IT guy left shortly thereafter; he was really too bright for the job he had. I never thought about that router, but it wasn't long before somebody needed to extend a few machines at an inconvenient spot and used that "hub" to accomplish it. A few machines managed to get their ip address and gateway from that old router, but of course couldn't get out to the internet any more, and it and the real router squabbled over their own ip, as did machines that got the same ip from different routers. Damn mess, but I found it pretty quickly, chastised the responsible party, and told them not to do that again.

Yeah, like that's going to work. A few months later it happened again. Different part of the building, but the same old router reincarnated as a "hub". This time I put a sign on it: "This is a router - it cannot be used as a switch or a hub". I figured that would keep it safe. Nope. Three months later it turned up again. Different culprit, and the sign mysteriously missing. I Scotch-taped the hell out of that note; somebody worked hard to take it off.

This time I went to an old hand at the plant. I explained again what had happened, and he shook his head in sympathy. "You know", I said, "it would have been better if somehow this had accidentally been thrown away. Like maybe if it just got bumped off the edge of this desk and landed in the trash.."

I turned my back and walked away. As I reached the door I heard a soft thump, perhaps made by something small landing in a partly filled wastebasket.. or perhaps not. We'll see.


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