Routers and switches and hubs, oh my!
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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