Get physical MAC address

Get physical MAC address

[Theewara Vorakosit]

Hello,

I get MAC address from ioctl. However, ifconfig can change this  MAC 
address. Can I get a real physical MAC address of the NIC?

Thanks,
Theewara

Re: Get physical MAC address

[Bernd Petrovitsch]

On Mon, 2007-12-31 at 12:39 +0700, Theewara Vorakosit wrote:
[...]
> I get MAC address from ioctl. However, ifconfig can change this  MAC 
> address. Can I get a real physical MAC address of the NIC?

- You can get the initial MAC address right after bootup before anyone
  changes it.
- Some (if not many if not all) of the drivers output it on
  driver initialization time so you could read it from `dmesg` or
  some /var/log/messages or .....
There is no "get initial MAC address" ioctl (but it's not that
complicated to implement it).

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services

Re: Get physical MAC address

[Stephen Hemminger]

On Wed, 02 Jan 2008 00:07:28 +0100
Bernd Petrovitsch <bernd@firmix.at> wrote:

> On Mon, 2007-12-31 at 12:39 +0700, Theewara Vorakosit wrote:
> [...]
> > I get MAC address from ioctl. However, ifconfig can change this  MAC 
> > address. Can I get a real physical MAC address of the NIC?
> 
> - You can get the initial MAC address right after bootup before anyone
>   changes it.
> - Some (if not many if not all) of the drivers output it on
>   driver initialization time so you could read it from `dmesg` or
>   some /var/log/messages or .....
> There is no "get initial MAC address" ioctl (but it's not that
> complicated to implement it).
> 
> 	Bernd

There is already ethtool interface to get what you want (ETHTOOL_GPERMADDR)


-- 
Stephen Hemminger <stephen.hemminger@vyatta.com>

Re: Get physical MAC address

[Jon Masters]

On Mon, 2007-12-31 at 12:39 +0700, Theewara Vorakosit wrote:

> I get MAC address from ioctl. However, ifconfig can change this  MAC 
> address. Can I get a real physical MAC address of the NIC?

Forgive me reading into your mail...this smells a bit like some kind of
licensing/compliance thing. Just bear in mind that using the MAC to
verify the identity of a machine is utterly useless and pointless -
anyone can trivially fool your software[0] to see what it "wants".

Jon.

[0] We used to have to do far worse kludgery in college, in order to
prevent the silly powers that be who "banned" network cards other than
those made by one manufacturer from being used on their little network.

Re: Get physical MAC address

[Kyle Moffett]

On Jan 01, 2008, at 21:42:18, Jon Masters wrote:
> On Mon, 2007-12-31 at 12:39 +0700, Theewara Vorakosit wrote:
>> I get MAC address from ioctl. However, ifconfig can change this   
>> MAC address. Can I get a real physical MAC address of the NIC?
>
> Forgive me reading into your mail...this smells a bit like some  
> kind of licensing/compliance thing. Just bear in mind that using  
> the MAC to verify the identity of a machine is utterly useless and  
> pointless - anyone can trivially fool your software[0] to see what  
> it "wants".

Not necessarily;  I can easily see distros wanting to have a "Restore  
defaults" button in their network config windows which also includes  
restoring the default MAC address to the NIC.  It should also be  
pointed out that anybody with one of a selection of re-flashable NICS  
(or NICS with removable EEPROMS) can easily change the MAC address on  
their NIC.  Other alternatives includes renaming eth0 to mynet0 and  
creating a downed dummy interface called "eth0" with the desired MAC  
addr.


> [0] We used to have to do far worse kludgery in college, in order  
> to prevent the silly powers that be who "banned" network cards  
> other than those made by one manufacturer from being used on their  
> little network.

Well for basically any userspace-level check, all it takes is  
somebody who knows ASM and has about 5 minutes to track down the  
problematic branch instructions.  Then they just have to write a 10- 
line GDB script which starts the program, traps the appropriate  
instructions, and then changes a "0" to a "1" (or vice versa) before  
the conditional branch.  On Windows it's vaguely practical (albeit  
crash-prone) to load a kernel hack which prevents your program from  
being debugged, but under Linux it's effectively impossible

Cheers,
Kyle Moffett

Re: Get physical MAC address

[Matt Domsch]

On Mon, Dec 31, 2007 at 12:39:11PM +0700, Theewara Vorakosit wrote:
> Hello,
> 
> I get MAC address from ioctl. However, ifconfig can change this  MAC 
> address. Can I get a real physical MAC address of the NIC?

yes.  It's ETHTOOL_GPERMADDR to the ethtool ioctl.

        case ETHTOOL_GPERMADDR:
                rc = ethtool_get_perm_addr(dev, useraddr);
                break;

When the driver is first loaded, before ifconfig can change the MAC
address, the existing (permanent) MAC address is stored away, able to
be retrieved via this ioctl.  Jon Wetzel, a Dell intern of a few
summers ago, wrote the code and was able to have it included.

Thanks,
Matt

-- 
Matt Domsch
Linux Technology Strategist, Dell Office of the CTO
linux.dell.com & www.dell.com/linux

Re: Get physical MAC address

[Bernd Petrovitsch]

On Die, 2008-01-01 at 22:58 -0600, Matt Domsch wrote:
> On Mon, Dec 31, 2007 at 12:39:11PM +0700, Theewara Vorakosit wrote:
> > Hello,
> > 
> > I get MAC address from ioctl. However, ifconfig can change this  MAC 
> > address. Can I get a real physical MAC address of the NIC?
> 
> yes.  It's ETHTOOL_GPERMADDR to the ethtool ioctl.
> 
>         case ETHTOOL_GPERMADDR:
>                 rc = ethtool_get_perm_addr(dev, useraddr);
>                 break;
> 
> When the driver is first loaded, before ifconfig can change the MAC
> address, the existing (permanent) MAC address is stored away, able to
> be retrieved via this ioctl.  Jon Wetzel, a Dell intern of a few
> summers ago, wrote the code and was able to have it included.

I stand corrected.
Last time I looked for such a thing it didn't exist.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
mobil: +43 664 4416156                 fax: +43 1 7890849-55
          Embedded Linux Development and Services

Re: Get physical MAC address

[Bodo Eggert]

Theewara Vorakosit <thvo@hpcnc.cpe.ku.ac.th> wrote:

> I get MAC address from ioctl. However, ifconfig can change this  MAC
> address. Can I get a real physical MAC address of the NIC?

First, get a network card having a physical MAC. Most cards have only a
(currently configured) default MAC address, maybe you'll be lucky
with some old ISA cards ...

Then, don't worry about sb changing it, since these cards don't support that.