Randomly Changing MAC Address

[Geoff Lane]

I'm hoping that the 'hardware' groups may be able to assist as I've
had no answers from Networking groups.

I use a mixture of Linux Mandrake, Win98, ME and XP. I have a wireless
network with Netgear WG602 54mbps AP, Netgear WG602 54mbps PC card, a
Linksys 11mbps USB adapter and a WiFi enabled handheld.

I've got a strange problem with a constantly changing MAC address on
my Netgear PC card.

I bought the Netgear AP and PC card in September this year, I set MAC
access for security. After a couple of weeks the Netgear PC card would
not access the network, all others OK.

Eventually I narrowed it down to a constantly changing MAC address
every time I switched the computer on.

Contacted Netgear and after consultations with technicians the card
was replaced under warranty.

Replacement card worked fine for a couple of weeks then again the MAC
address srarted changing each time I switched on.

Card again replaced under warranty.

Third card, after a couple of weeks being OK is now doing exactly the
same (Not yet returned).

Provided I turn OFF the MAC access the card still works OK.

First six HEX digits always 02-10-91 but the last six always change
every time I restart the computer.

I've tried the cards in different computers and still the same
problem.

Any clues would be appreciated.

Geoff Lane
Welwyn Hatfield Computer Club - Hertfordshire, UK
www.whcc.co.uk - Online facilities for non locals

 

[Phrederick]

I'm hoping that the 'hardware' groups may be able to assist as I've
had no answers from Networking groups.

I use a mixture of Linux Mandrake, Win98, ME and XP. I have a wireless
network with Netgear WG602 54mbps AP, Netgear WG602 54mbps PC card, a
Linksys 11mbps USB adapter and a WiFi enabled handheld.

I've got a strange problem with a constantly changing MAC address on
my Netgear PC card.

I'd hit the Linux support groups for this one... Most likely a configuration
option.

 

[Geoff Lane]

I'd hit the Linux support groups for this one... Most likely a configuration
option.

I did actually cross post to a Linux group as I find Linux users very
technically minded.

I don't think it is a configuration problem as I have tried the card
in another machine with the same result.

I understand MAC addresses can be spoofed but I don't think they can
be physically changed.

Geoff Lane
Welwyn Hatfield Computer Club - Hertfordshire, UK
www.whcc.co.uk - Online facilities for non locals

 

[Phrederick]

I'm hoping that the 'hardware' groups may be able to assist as I've

I did actually cross post to a Linux group as I find Linux users very
technically minded.

I don't think it is a configuration problem as I have tried the card
in another machine with the same result.

I understand MAC addresses can be spoofed but I don't think they can
be physically changed.

Physically changed, no... The OS use a different MAC than the one on the
card, yes.

On a Windows XP machine, go into your LAN properties... into the NIC
configuration screen, to the Advanced tab. You'll usually see a "managed
address" or "network address" option here. This allows you to put any MAC
address you want and the OS will use it.

There are a big batch of ASUS mainboards that were sold with an SiS onboard
LAN chip. Every single one has the same MAC address. The only fix is to
alter the MAC in the network settings as above. I think the bad MAC ends in
55:66 .

 

[Joe Pfeiffer]

Physically changed, no... The OS use a different MAC than the one on the
card, yes.

No, when you change the MAC address, you are changing the address the
card responds to on the wire. That's as "physically changed" as it
gets, even though you're changing firmware.

On a Windows XP machine, go into your LAN properties... into the NIC
configuration screen, to the Advanced tab. You'll usually see a "managed
address" or "network address" option here. This allows you to put any MAC
address you want and the OS will use it.

That sounds a lot like the IP address (though I don't use Windows, so
I can't really be sure).

There are a big batch of ASUS mainboards that were sold with an SiS onboard
LAN chip. Every single one has the same MAC address. The only fix is to
alter the MAC in the network settings as above. I think the bad MAC ends in
55:66 .

What on earth were they thinking???

 

[Joe Pfeiffer]

Sorry to followup my own post, but right after sending I came across
how to set MAC addresses under Linux: it's a parameter to ifconfig,
as in "hw ether yo:ur:ma:ca:dd:rs". More information is in the
ifconfig man page.

Note that you can't have two interfaces on one subnet with the same
MAC address!

 

[Peter]

No, when you change the MAC address, you are changing the address the
card responds to on the wire. That's as "physically changed" as it
gets, even though you're changing firmware.

No, of course it isn't. You can't change any physical MAC Address under
normal cirumstances.
Networking would be one big mess ha!ha!
What is changed is the MAC Address list in the Netgear WG602 , that's
something else than changing a physical address
Purely done for security reasons.
Phrederick seems to know what he is talking about, unlike you

 

[kony]

No, of course it isn't. You can't change any physical MAC Address under
normal cirumstances.

So often there are exceptions, and they always seem to pop up when you
least expect...

Most motherboards can have the MAC changed, and at least a few
(thinking of PCChips) gave the end-user access to it. That's pretty
significant today with more and more boards having integrated
adapters.


Dave

 

[Geoff Lane]

No, of course it isn't. You can't change any physical MAC Address under
normal cirumstances.
Networking would be one big mess ha!ha!
What is changed is the MAC Address list in the Netgear WG602 , that's
something else than changing a physical address
Purely done for security reasons.

I'm getting confused here, your last comment, are you referring to the
MAC address list that allows (Or denys) access for VICs with specific
MAC addresses?

From the answers here it does look as though I've got a dodgy card and
as it is the third one giving the same fault it may appear that
Netgear have a problem somewhere.

Geoff Lane
Welwyn Hatfield Computer Club - Hertfordshire, UK
www.whcc.co.uk - Online facilities for non locals

 

[Joe Pfeiffer]

Yes, you can. I was pretty shocked to find out that yes, you can
indeed change the "physical" MAC address; you are right that if you
set two cards on the same subnet to the same MAC address, chaos will
ensue. The "hw" option on ifconfig really works just like the man
page says it does.