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Old 12-06-2017, 02:07 PM   #1
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wifi card MAC changes undesirable randomly

Hello there,

a couple of weeks ago I encountered problems with my wifi connection.
It suddenly stopped being connected and any attempt of reconnect it failed.
Since we shortly got a new router from our provider I thought our new send router isn't able to handle linux and windows systems in the same network in the right way. But these are not the times for problems like this anymore, especially for the reason that we never had problems with our old router before.

And here it comes:
After some attempts I found that the MAC address of my wifi card is not correctly shown in the config menu of the wifi connection (i use ubuntu 17.04) and my router is probably refusing the attempt to reconnect.
I wondered how it came and while trying to analyze the problem it changed after some time randomly to another MAC address. Ten minutes later everything was normal again.

I am not deep into security stuff and have almost no experience with analyzing problems like this. I started to search the internet for similar problems but the only thing I found was an unsolved threat in some forum. Again my connection broke down and I took my second laptop (with ubuntu 16.04) and spent half the night finding a solution. And surprisingly the same happened with the other laptop, too, after some minutes.

I have to tell you that I can use

sudo ifconfig eth0 down
sudo ifconfig eth0 hw ether [my real MAC] 
sudo ifconfig eth0 down
to solve the problem for a short period of time (some seconds up to some minutes) and after retrying a couple of times I solve it for longer,
but I want to know WHAT THE HELL IS GOING ON?
How is it possible that things like this can happen?

The problem appeared randomly in the last weeks, maybe four or five times at all. The first time it was really penetrant.
I don't have macchanger or anything similar. There is no reason for me to change my MAC address. I thought it could be a direct intrusion, but since I have not much of a plan I have no idea for what reason or if it is even likely enough to think about it.

I used rkhunter and chkrootkit and also the wireless-info script, but to be honest I had quite problems of interpreting the outcome, especially for the last one. The other two gave no results except for the known false positives.

Now I want to know how you would start with this problem.
Where to look for logs etc. to find something of interest?
I have no idea.

Thanks for reading.

Old 12-06-2017, 02:40 PM   #2
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Welcome to LQ.

Something's fiddling the Mac address. It could be in your new router. FYI, the Mac address is traceable to your Box so 'spoofing' the MAC address is a good security technique, but a PITA as you can see. Look for logs in /var/log, or the output of
sudo dmesg |less
Also worth a shot is
lsof |grep wlan0
That presumes your wifi card is wlan0 - replace with what yours is called. I just see dhcpcd and wpa_supplicant
Old 12-06-2017, 02:59 PM   #3
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This is a "feature not a bug" of Network Manager v. 1.4.0 and newer.

If you don't like this feature, you can disable it as follows:

Edit your /etc/NetworkManager/NetworkManager.conf file and add the following code:

More info here:
2 members found this post helpful.
Old 12-06-2017, 04:42 PM   #4
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Hello and welcome to LQ.

I think it's a bit silly to default to mac changer like that but the router should have still worked unless it ran out of leases or you set a preferred mac assignment sort of deal.
Old 12-06-2017, 05:12 PM   #5
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Thank you for the quick answers.
I guess sometimes one has to dive deep to improve the swimming skills (with water wings).

I didn't set a specific MAC in my routers configuration, so I think it is the standard behavior of the router to identify mac-spoofing. I will investigate this later and also how this thing interacts with my system.

Last edited by hunhunhun; 12-06-2017 at 05:32 PM.
Old 12-07-2017, 03:24 PM   #6
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I doubt a common home router can detect mac-spoofing.


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