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Wireless Lan connection issue with Linux clients

Hi

In a large Wireless Lan enviroment for a university, we have 3 WISM moduls attached on a 6k hw - Manged by ACS v6.0.181.0

We recently upgraded the software version of the controllers from 4.x to 7.0.98.0 - the Emergency Image version is 5.2.157.0

Since then, the students with Linux clients have massive connection issue - repeated connection lost in a short time period.

However the students with Windows clients have no problem at all.

The studends report, that their linux clients getting so much of some kind of unnecessary broadcast traffic which can not be handled by the NIC - and the NIC goes down - and this happens all 5-10 minutes.

Affected Linux clients are: Ubuntu v10.10 - also OpenSuse, Fedora and Arch-linx with latest OS version.

Any Idea how I could solve this problem?

Thanks in advance for your help

5 REPLIES
Cisco Employee

Re: Wireless Lan connection issue with Linux clients

Hi,

few questions :

-What kind of broadcast traffic are the clients receiving exaclty ? knowing that might help to solve the problem

-Do you have "Broadcast Forwarding" enabled or disabled in the general WLC options ? If it's disabled, it means that broadcasts are blocked from wired to wireless, so I doubt your clients would be receiving any broadcast at all actually.

Nicolas

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New Member

Re: Wireless Lan connection issue with Linux clients

Hi Nicolas

Thanks for your reply. The broadcast forwarding is disabled on WLC's.

Pls find below the attached picture, which shows the captured broadcast traffic on a linux client (sent by a student to me).

I'm not sure, if its really only the broadcast traffic, which the linux clients can not handle.

From my point of view, it seems also to be that the linux clients are somehow disadvantaged among the other clients like windows or mac, if they all trying to get a wireless connection.

But the fact is only the linux clients are affected - and this happens to the linux clients only in our wireless infrastructure.

Windows or Mac clients have no such problem at all

regards

Enis

Cisco Employee

Re: Wireless Lan connection issue with Linux clients

Hi Enis,

it seems you have a /16 subnet for your wireless clients ? That's maybe a bit large.

I would look at 2 options :

check why the .254 is not replying to ARPs (as seen in the sniffer trace)

Create several subnets for the wireless client. That will reduce ARP traffic a lot.

Nicolas

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New Member

Re: Wireless Lan connection issue with Linux clients

Hi Nicolas

We use a /19 subnet (not a /16) - .254 is the gateway of this subnet, which is always up and replying. (don't know why it wasn't replying on this picture)

Anyhow, It doesn't explain why the linux client connection issues began after software update of the controllers. - Withe the old OS, there were no such issues.

regards

Enis

Cisco Employee

Re: Wireless Lan connection issue with Linux clients

Indeed.

It would take more complex troubleshooting to check where the ARPs come from and why there is that many.

Reducing subnet size is a workaround.

Maybe there is the same amount of ARP with windows clients but they are less affected ? or for some reason they don't receive the ARPs.

I think it would take some deep troubleshooting to fully understand.

Nicolas

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