Ethernet mac address changing randomly
 

I'm using Debian wheezy with kernel 3.2.0-4-686-pae but sometimes my mac address is changing randomly. Really I didn't find anything that could be chinging mac addr within my /etc/init.d/ scripts.
Now I tried to settle mac address within /etc/network/interfaces, but I'm not sure if it will fix it.
I need mac addr to remain always the same as long as I use wake on lan feature.

Any ideas on why mac address could be changed randomly?

Thanks!

the MAC address on a NIC can not change. do you have more then one NIC in your system? it could be that eth0 is swapping between the different NICs.

Yes, this is what is happening. Debian, by default, uses dynamic assignments for network interfaces.

are you talking about my response with multiple NICs in his system?

Yes, I found this behaviour weird, as long ethernet mac address should not change, but it's changing. I only have one NIC in this box.
Is there any way to disable this "dynamic" assignment of mac address? I couldn't find anything within /etc/init.d/ sysv scripts.

Thanks for your answers, regards-

How do you know it is changing?. Can you show/explain really how you confirmed MAC address is changing?.

Are you using a Virtual machine?? KVM, vmware, virtual box?

Yes how do we know the MAC ADDRESS is actually changing?

Do an ifconfig and get your MAC ADDRESS, reboot the system and get the MAC ADDRESS again. Did it change on reboot?

Or have you got something strange going on with UDEV? Look in here for any extra rules especially under network.

You can set your MAC ADDRESS statically with ifconfig:

Get someone here using Debian to confirm your /etc/network/interfaces file it looks a bit whack.

I think you are getting confused here, why are you doing the folowing?The MAC address is a hardware address built into every network card which ordinarily will never change. It does not need to be changed by you unless you have a specific reason to do this. If you want to use Wake on LAN you do not need to give your card a MAC address you need to make note of hthe MAC address given in ifconfig without trying to set the MAC address as you do above and use that MAC address to wake the machine.

Thanks for your feedback folks.
I noticed my mac addr was changing cos' I'm using wakeonlan feature, using wakeonlan program that pacakage the "magic packet" (ethernet frames for wol) within an udp datagram. Everything works fine for a while, but then I found a change with mac address and it stops working.

As long as hardware mac address could not change (it can only be "faked" by software). For the udp to reach my machine I had to do a "mac-binding" in my router (tp-link). This is adding a fixed entry within router's ARP table as far as I'm concerned. That way udp datagram can reach the final destination.

I added those entries within my /etc/network/interfaces just to try if that way mac addr remains settled.

do an :

make sure you have no more interfaces then you think.

cat
Or the Debian equivalent and check for inconsistencies.

Is the MAC address usually one of 2 addresses or is it RANDOM everytime? Do some restarts collect some stats.

Hi gdizzle,

There's only one nic in this box. And nothing appears strange with udev rules.
I'll do some tests and try to check if there's something tricky with the router and the WOL stuff.

Thanks!