Source
r/cmu•
bricksoup

So, really, what's the deal with the CMU wireless and Linux machines?

I saw the posts about the wireless questionnaire, and I was wondering how many people are really affected by this thing? 8 times out of 10, my T410 with Ubuntu fails to connect. Everyone I know reports the same - even professors and TA's. Windows works just fine. Are we all dealing with this, or what? Is there a Linux user who doesn't have issues? Is there someone who did have issues, but successfully resolved them?

It's driving me up the wall. I've been unable to print homeworks a couple times now (fool me once...), and I've had a ton of problems collaborating with my groupmates. Computing services' response is essentially "FU."

Posted Nov 26, 2011, 7:06 AM UTC

1916
tylerni7•

So one of the major issues that Linux has is really more of CMU's fault. More accurately the fault of whoever makes our access points (I forget if they are Cisco or someone else).

Basically the way the are set up, if you try to connect to them, they attempt to do a special form of load balancing. So they will reject your connection, and then point you to the router to which they want you to connect. The problem is.. this isn't actually in the 802.11 spec. To deal with computers that don't follow the spec, the access points will basically allow a computer to connect after it tries to connect 3 times, as it will assume the computer doesn't understand the router's suggestion to go elsewhere.

A lot of OSs, Windows, OSX, and even Android, either implement the slightly broken, but compatible version of the spec, or they will try connecting to the same router at least 4 times. The issue is that Linux not only does not implement this modified spec, but also will fail after trying to connect 3 times. That means if you try connecting enough that you hit 4 times on a given access point, you should get connected. Until then though, you'll have lots of problems making the connection.

The solution is to use a magic patch for WPA supplicant (yea I know your connection doesn't use WPA, but the wifi driver makes use of it), which will allow this to work. I don't know where this magic patch is, sadly, but it is out there!

I've had this explained to me by a friend, so I don't remember all of the details, but that should be reasonably accurate. If I find the patch I may throw up a link on r/cmu since I'm sure lots of people have had this issue.

14
bricksoupOP•

This would explain the randomness of my connectivity. Thanks for the very helpful info.

2
jmmcdermSenior (CS)•

This. Also, for me at least, it is limited to academic buildings i.e. it works fine in my dorm, so that seems to confirm that it is related to the vendor. I wish I could find that patch, especially since Android and ChromeOS both seem to have it.

2
masqueradestarAlum (CS '13, Philosophy '13)•

Have you found the patch?

1
tylerni7•

No :|

I'll try to bug the guy who told me about this, and see if he can either tell me enough about the problem that I can patch it myself, or to see if he can find the fabled patch himself.

I've bugged him once or twice since this post about it, but he couldn't seem to find it. He's currently a grad student who lives out of state, so I don't get much of a chance to ask him about it.

I'll try to work on it though, sorry I haven't been able to come up with anything :(

Edit: there is a chance it is in the latest version of wpa_supplicant in git. I'll try to let you know if this seems to be the case.

1
[deleted]•

[deleted]

1
killafreeze•

Hey, gang. We are not familiar with any widespread CMU cleartext Vs Linux problem, but we'll be glad to help. We routinely have to work with the AP vendors (Aruba Networks and/or Xirrus) on specific driver issues. For example: every lenovo laptop in tepper suddenly was hosed by a certain driver update, folks had to revert driver to use wireless. I would suggest OP send an email to advisor@andrew and ask to have your issue "escalated to NetOps, Randy said so". We'll be glad to troubleshoot this with you. I did find it interesting that using WPA setting was mentioned as a fix. MAybe you can connecting to CMU-SECURE (our brand new WPA SSID) as a workaround? details here:http://www.cmu.edu/computing/network/connect/wireless/secure/index.html (note: Check out the "General" section for basic linux config)

TLDR: CMU NetOps is here to help. Give us a call!

7
jmmcdermSenior (CS)•

CMU-SECURE does seem to actually work from the location I am in currently, however I had to first extract the root certificates from an old install of ubuntu, since I couldn't find a working link to them on cmu.edu anymore, and the default connection manager in Ubuntu didn't seem to be able to acquire them automatically.

2
duruqAlum (Cog Sci, HCI '10)•

Hey guys. I know one of the CMU NetOps people and I talked to him on Twitter, sending him this thread. He immediately replied and said that "he'll look into trouble reports wherever he finds them".

He has been extremely helpful to me in the past so I have no doubt that he'll look into this. If nothing comes up in a week or two, feel free to PM me and I'll check with him again.

5
masqueradestarAlum (CS '13, Philosophy '13)•

Reminding you 'bout this.

2
duruqAlum (Cog Sci, HCI '10)•

So what's the issue?

1
masqueradestarAlum (CS '13, Philosophy '13)•

See original post...

2
masqueradestarAlum (CS '13, Philosophy '13)•

I posted about this here ages ago... to no avail, sadly. :\ Still have trouble connecting my T400 to wireless. Funnily enough, as of late it seems to depend on location: Gates seems to work fine, but the connection is bad enough in Wean that I don't even bother.

4
deepcube•

are you having trouble in the dorms or on campus? different wifi vendors

2
bricksoupOP•

Campus. Inside, outside, everywhere on campus.

I have no experience with the dorms personally, but now that I think of it I do have a friend who says he's not able to connect inside West Wing.

2
AltacoSenior (CS)•

I've never had a problem.

2
metalforever•

I use slackware linux and do not have any issues.. using a t42

2