Why doesn't her laptop work on one Ethernet port?

September 19, 2006 11:10 AM

My daughter's college dorm room has two Ethernet ports, and her laptop interacts with them differently. I can't understand what's going on, so I'm asking the hive mind.

When I first plugged her laptop into the port next to her bed, Windows Home on her new HP Pavilion dv2000 reported "network or cable unplugged." So I tried a different cable, and still a third and a fourth. All received the same error.

Three other computers, using those cables, plugged into the port just fine. Two Macs and one Windows Pro SONY.

So I purchased a USB Ethernet dongle for her, thinking maybe her laptop's ethernet port was bad. Same error.

However, if we plug her computer into her roommate's port, it connects fine.

So they're in a weird arangement where long cables cross the room, and each is plugged into the other's port.

What could explain this bizarre problem? Help a computer-wise Dad regain credibility with his daughter.

posted by cameradv to computers & internet (21 comments total)

Your daughter's port may have accidentally been wired with one or more wire pairs reversed, and your daughter's laptop (and USB dongle) don't have auto-sensing port polarity logic. Try plugging a cheap Ethernet 10/100 mbit switch into the port, for its auto-sensing uplink port, and your daughter's laptop into the switch. If it works, you've proved my theory and given your daughter 4 extra ports for LAN parties. If it doesn't, you return the $30 switch to CompUSA.
posted by paulsc at 11:18 AM on September 19, 2006

Is by chance, her roommate using a Mac? I'm fairly certain that if the port has been mis-wired (basically into a flipped crossover connection) a normal PC wouldn't detect a network, but one with an auto-sensing Ethernet port (like a Mac) would be able to reconfigure itself to handle the flipped connection.

Confirmation of this theory would require a device for testing for properly wired Ethernet (the Network guys at her school should have one of these).
posted by onalark at 11:23 AM on September 19, 2006

On Preview: paulsc and I have the same theory, but different proposed solutions.
posted by onalark at 11:24 AM on September 19, 2006

I, too, think that the port is likely to be miswired as a crossover port, the only explanation which would allow the two Macs to use it (since all Macs have autosensing ethernet ports which can handle standard and crossover ports). (And I bet that the Sony PC also has an autosensing port, whereas your daughter's HP Pavilion laptop doesn't.)

If that's the case, let me throw out there a third possible solution: a crossover dongle, six bucks plus shipping, and it's nice to have around in any event!
posted by delfuego at 11:34 AM on September 19, 2006

(Note that if your daughter's school is hip to the gigabit ethernet world, then you'll want a gigabit-capable ethernet crossover dongle, which'll run you a whole buck more. Hell, it's worth it in any event -- if the wiring's not gigabit, then this will work just fine, and it's future-proof.)
posted by delfuego at 11:36 AM on September 19, 2006

It could also be a speed/parity setting. It's possible your daughter's laptop is set to manually pick a speed (10/100/1000) or parity (full/half) and the roommate's switch port is set compatibly. Try going into the network properties for your daughter's ethernet connection and making sure that the speed/parity is set to auto.
posted by FYKshun at 11:41 AM on September 19, 2006

So they're in a weird arangement where long cables cross the room, and each is plugged into the other's port.

Could they not just swap sides?
posted by influx at 11:49 AM on September 19, 2006

Another solution is a wireless basestation plugged into one of the ports and then location doesn't matter (assuming that both computers have wireless cards).
posted by HuronBob at 12:08 PM on September 19, 2006

Why not check with the college's tech support team?
posted by kenchie at 12:41 PM on September 19, 2006

To elaborate - I work in IT on a college campus. There could be port security issues within the switch - only the network admin will be able to fix this so just ring the helpdesk and ask!!!
posted by kenchie at 12:47 PM on September 19, 2006

huronbob: a wireless basestation is a BAD idea in a college dorm. The IT folks are likely to notice and kill the port fast...they don't want anything interfering with the wireless that they (probably) already have. Plugging in a wireless router is likely to cause loopback problems and cause the network to go very wonky.
posted by griffey at 12:49 PM on September 19, 2006

Thank you all. A mis-wired socket is a likely problem, and a crossover dongle is the likely solution. I'll try it out. I thought modern ethernet ports would have similiar capabilities.

Roommate dynamics make it hard to switch room sides.

The college support team just plugged a Mac in and said "It's all good" but this is probably something they could fix. They did spell out the process for "certifying" a wireess router, but it scared my daughter, so we won't go that route.

I did check that her computer is set to "Auto" for the settings.

Best answers after confirmation ...
posted by cameradv at 12:58 PM on September 19, 2006

If network infrastructure isn't working call the campus help desk. There isn't any reason to either mess with this or spend money.

HuronBob writes "Another solution is a wireless basestation plugged into one of the ports and then location doesn't matter (assuming that both computers have wireless cards)."

If you do this on my campus the network port serving the wireless access point is automatically shut off. Which maybe cameradv's daughter's problem. The ports were shut off for abuse by the former tenants and haven't been turned back on.

On preview: I wonder if it was tech that plugged the Mac in or the dorm manager. If the later the network guys should still come out.
posted by Mitheral at 1:16 PM on September 19, 2006

I work in CIT at a moderately big university in the northeast. I'm sure the pr folks would love it if I said major research university or some such nonsense but that's their problem. I have previously worked on the help desk at a smaller college and participated in too many "resnet" start-up events.

Step 1. Your daughter, not you, needs to get ahold of the help desk and/or resnet folks. We appreciate your concern but your daughter, not you, is the person we need to work with. Feel free to coach her, give her a script, whatever makes you happy. Calling the help desk yourself isn't likely to help the situation.

Step 2. Step back. No, seriously. Step away from the computer and the phone. Yes, we understand this is a major crisis. Yes, we know that she cannot instant message you, her mother, or her 400 closest friends. Nor does she have access to important academic resources. Yep, got that message. And we want to help.... her.

The best thing you can do is encourage your daughter to step up to the plate and call IT.

Ok, so you want to know what's going on behind the scenes? Could be a zillion things. For starters, the networking folks have the network tied up in more ways than you can imagine. There's probably a firewall between resnet and the campus. There's probably a "registration" system on resnet that looks for common problems (google "NetPass" (not the pr0n service). And there's probably a weird quirk that's preventing her from getting online. Like perhaps a firewire port that's advertising as a network connection. Or the wireless in her laptop is bridging to the wired connection.

Really, have her call the help desk. They're there for a reason.
posted by jdfan at 1:51 PM on September 19, 2006

(Tiny correction to FYKshun's comment: you're probably thinking of duplex (full/half), not parity. Parity doesn't really apply to ethernet, and even if it did, it would be even/odd/mark/space/none, not full/half.)

There are weird cases where autosensing can be a problem, if the equipment at each end can support a high speed, but the cable between them can't. Then the equipment autosenses a high speed but can't communicate at it. This could be the case if the roommate's machine can't go to as high a speed as the daughter's machine, and there's something wrong with the dorm wiring.
posted by hattifattener at 7:15 PM on September 19, 2006

Call the help desk. They may not even have the port plugged into the patch panel.
posted by cellphone at 7:50 PM on September 19, 2006

Could be network be using MAC filtering? You should call the helpdesk.
posted by Mr. Gunn at 8:48 PM on September 19, 2006

The only way it could be MAC filtering is if it was an exclusion, which is very unlikely. We know that because of all the other computers that have worked.

We also know that the port must be plugged in, turned on, working, etc. For the same reason.

If anything, all the "I work in university networks" people are making the help desk option less attractive.

But much more interesting than all that, really, do you think there is any difference between the gigabit crossover dongle and the regular one? I very much doubt it!
posted by Chuckles at 10:44 PM on September 19, 2006

jdfan: Let me be sure I understand ... I should step away from the child and let her solve the problem? :-)

I get that, I'm not trying to "helicopter" too much. But when I was there, I _did_ call the help desk. They checked the port was plugged into the wiring closet and they sent the guy with the Mac who said "no problem." No one plugged any socket tester into the wall socket.

Anyway, my proposal was for her to (1) re-call the help desk to get the socket checked out and (hopefully) re-wired. If no satisfaction there, (2) try the mail-order dongle. Finally, when I go to visit parent's weekend, I'll take a cross-over cable with me.
posted by cameradv at 8:39 AM on September 20, 2006

cameradv: I have to second what someone else above said... just b/c someone "checked the port" doesn't mean a whole lot.

Yes, re-call the help desk. Keep the problem open until it's actually resolved. Don't step away from the child so much as let her be the agent.

Don't bother with mail-order dongle or cross-over cable. You're only adding complexity to the issue and there's no reason you should fix their (the college's) problem.

If the HD has half a clue, they'll ask your daughter to bring her laptop in and check it on a known-good port they have in their office expressly for this purpose.

Our ResNet students must register their computer to gain access to the outside (of the dorms) network. The system requires a scan for obvious signs of certain vulnerabilities, root kits, etc. It also notices if there are multiple MAC addresses advertising from the computer, if there's evidence of bridging (from wired to wireless) and a few other things. If she hasn't registered, she's not going to get anywhere. In all likelyhood, her MAC address may be locked out.

So, have her follow up w/ the Help Desk until they fix it.

If they can't seem to resolve it (or it seems to be taking an especially long time on their part), then I suggest escalating it to someone a little higher... like the HD manager. Give the HD manager a chance before going higher.

BTW, the someone who check the port was, in all likelihood, a student. And as much as we try to train them to know everything, they don't.
posted by jdfan at 8:16 AM on September 25, 2006

one more thing... you could also email this page to the HD manager at your daughter's school :)
posted by jdfan at 8:19 AM on September 25, 2006