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View Full Version : Nightmare - Multiple MBA on Network - Duplicate MAC addresses




lelandv
Mar 3, 2013, 10:44 AM
Could someone enlighten me as to which complete idiot at Apple decided that it would be a good idea to use the same MAC address for multiple MBAs ??

We have three users with MBAs (each purchased separately and not as a bundle). All three of them have the same MAC address for the airport/wifi interface, and for the wired Gig-E adapter, likewise, they all have the same MAC address.

The practical upshot of which is that when two or more users are connected on the same LAN, all hell breaks loose.

Can someone please shoot the imbecile at Apple who came up with that hair-brained idea? and on a more practical matter, what would be the best way to persistently assign a unique MAC to these interfaces on the MBAs?

I know that you can "spoof" or change the mac address using ifconfig, but is there a way on these things to keep it persistent, or at least automatic when the interface is brought up ?

Thanks


Leland



BigYellow
Mar 3, 2013, 11:26 AM
Could someone enlighten me as to which complete idiot at Apple decided that it would be a good idea to use the same MAC address for multiple MBAs ??

We have three users with MBAs (each purchased separately and not as a bundle). All three of them have the same MAC address for the airport/wifi interface, and for the wired Gig-E adapter, likewise, they all have the same MAC address.

The practical upshot of which is that when two or more users are connected on the same LAN, all hell breaks loose.

Can someone please shoot the imbecile at Apple who came up with that hair-brained idea? and on a more practical matter, what would be the best way to persistently assign a unique MAC to these interfaces on the MBAs?

I know that you can "spoof" or change the mac address using ifconfig, but is there a way on these things to keep it persistent, or at least automatic when the interface is brought up ?

Thanks


Leland


Are you positive? Check in the System Preferences->Network->Wi-Fi->Advanced tab, at the bottom of the screen that pops up, and then in System Information->Network->Wi-Fi.

The odds of two MBA's manufactured having an identical WLAN MAC address is slim enough, but three? And three Ethernet adaptors? And then all being sold to the same person?? I just can't see it.

lelandv
Mar 3, 2013, 11:34 AM
Yup...

Even between the MBAs tested, one was purchased in the US, the other in Germany. The users are trying to use them on the same LAN, and it's having some rather "CURIOUS" effects as I'm sure you can imagine.
We use static DHCP assignments for that end network as well, which doesn't help matters.

Essentially, MBA #1 and MBA #2, for example, both have b8:8d:12:53:26:14 for the gig-E adapter, and both have 60:c5:47:05:d0:1e for the airport/wifi.

This smells a lot like clone-production rather than carefully planned manufacturing.

Leland

theSeb
Mar 3, 2013, 12:19 PM
What you have described is *impossible*. In theory.

I am having a hard time believing that you have 3 MBAs that have the same MAC addresses. A MAC address is, by it's nature, a unique identifier. You have more of a chance of winning the lottery than finding 3 MBAs with the same MAC addresses. That makes me think that there is something else wrong with your network setup.

I would suggest to go into network preferences and removing your LAN/TB adaptor and then adding it again as a first step.

thasan
Mar 3, 2013, 12:24 PM
What you have described is *impossible*. In theory.

I am having a hard time believing that you have 3 MBAs that have the same MAC addresses. A MAC address is, by it's nature, a unique identifier. You have more of a chance of winning the lottery than finding 3 MBAs with the same MAC addresses. That makes me think that there is something else wrong with your network setup.

I would suggest to go into network preferences and removing your LAN/TB adaptor and then adding it again as a first step.

Exactly. I also thought they are unique? Maybe you are using a software which is setting up a MAC address for the use in network. And maybe the default in that software is the same MAC address which is causing the problem...

theSeb
Mar 3, 2013, 12:38 PM
Exactly. I also thought they are unique? Maybe you are using a software which is setting up a MAC address for the use in network. And maybe the default in that software is the same MAC address which is causing the problem...

Indeed.

media access control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet. Logically, MAC addresses are used in the media access control protocol sublayer of the OSI reference model.

MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, such as the card's read-only memory or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address.

Mrbobb
Mar 3, 2013, 01:17 PM
If u were in front of me, I'd put down a thousand$ buxs right now, on the table, that you don't have 3 (THREE) same MAC.

Most likely your switch is bad or needs a hard reset.

Dark Fiber
Mar 3, 2013, 01:24 PM
If u were in front of me, I'd put down a thousand$ buxs right now, on the table, that you don't have 3 (THREE) same MAC.
Most likely your switch is bad or needs a hard reset.
You might lose! There were separate reports of identical MAC addresses in consumer routers a few years ago.

lelandv
Mar 3, 2013, 02:02 PM
@theSeb : While under normal circumstances I would agree with you that it would be next to impossible to have the same MAC address on multiple machines, what we are seeing is indeed just that.

What is even more disconcerting is that the three MBA were purchased individually in different geographic locations, the most extreme being one in the US and one in Germany.

Nevertheless, System Preferences->Network and simply "ifconfig" show the MAC addresses as follows:

Airport/Wifi:
60:c5:47:05:0:1e for all three MBAs

Gig-E adapter:
b8:8d:12:53:26:14 for all three MBAs.


Indeed when doing "sh mac addr dyna addr xx:xx:xx:xx:xx:xx" on the cisco switch that they're connected to (in the wired scenario), three different ports are shown for the same MAC address, corresponding to the three ports that they are actually physically connected to...

This smells to me like someone simply trying to cut costs by CLONING on the production line...

L.

iphone46
Mar 3, 2013, 05:20 PM
@theSeb : While under normal circumstances I would agree with you that it would be next to impossible to have the same MAC address on multiple machines, what we are seeing is indeed just that.

What is even more disconcerting is that the three MBA were purchased individually in different geographic locations, the most extreme being one in the US and one in Germany.

Nevertheless, System Preferences->Network and simply "ifconfig" show the MAC addresses as follows:

Airport/Wifi:
60:c5:47:05:0:1e for all three MBAs

Gig-E adapter:
b8:8d:12:53:26:14 for all three MBAs.


Indeed when doing "sh mac addr dyna addr xx:xx:xx:xx:xx:xx" on the cisco switch that they're connected to (in the wired scenario), three different ports are shown for the same MAC address, corresponding to the three ports that they are actually physically connected to...

This smells to me like someone simply trying to cut costs by CLONING on the production line...

L.

Check the boxes and see if they are the same.

edjs
Mar 3, 2013, 06:58 PM
It beggars belief that three MBAs from different sources have the same MACs, without the issue coming up before now.

I'd be inclined to check that there are no startup items that might be setting the MAC address at boot.

If you look at About this Mac -> More Info -> System Report -> Network, it should show the burned-in MAC addresses. If they are the same there, you'll need to either set the MBAs to change the MAC at startup to something unique, or bring it up with Apple.

Hmm. Took another look and I see that System Preferences->Network also shows the burned-in MAC, even if I change the MAC with ifconfig. <shrug>

Makes no sense to me.

edjs
Mar 3, 2013, 07:12 PM
Adds a preferences pane that allows changing the MAC addresses:

https://github.com/halo/LinkLiar/

Mrbobb
Mar 3, 2013, 07:13 PM
It beggars belief that three MBAs from different sources have the same MACs, without the issue coming up before now.

If this is not widespread (google) then the problem is local.

lelandv
Mar 4, 2013, 02:09 AM
If this is not widespread (google) then the problem is local.

To be perfectly fair, I did google the problem, and the only things that I found that were somewhat related where situations where a site has thousands of MBAs to administer centrally, with hundreds of the gig-E adapters. The site using Casper, and omitting to flag the dongles as removable mac addresses, thus generating duplicates in the database....

We're mostly a Linux shop here, but we do have a few mac users... though have only ever encountered this issue with MBAs -- MBPs no problem.

Awaiting the more detailed information from the people concerned to check the BIAs via the "About this Mac" menus, and further diagnosis...


Leland

sero
Mar 4, 2013, 02:49 AM
It's easy enough to spoof the mac address. You could script it and have it run at startup/login, or triggered by an event. I basically do this when I want to physically connect to my work network.

swordfish5736
Mar 4, 2013, 09:01 AM
To be perfectly fair, I did google the problem, and the only things that I found that were somewhat related where situations where a site has thousands of MBAs to administer centrally, with hundreds of the gig-E adapters. The site using Casper, and omitting to flag the dongles as removable mac addresses, thus generating duplicates in the database....

We're mostly a Linux shop here, but we do have a few mac users... though have only ever encountered this issue with MBAs -- MBPs no problem.

Awaiting the more detailed information from the people concerned to check the BIAs via the "About this Mac" menus, and further diagnosis...


Leland




you say you are using ethernet on MBA's. Does each computer have its own thunderbolt->ethernet adapter? Are you using USB ethernet adapters?

Whatever type of adapter you are using is actually where the ethernet mac address is coming from, not the MBA itself.

have you tried connecting the computers to the same wifi network? Or did you just notice that they all show the same MAC address for wifi as well?

lelandv
Mar 4, 2013, 01:42 PM
Well.. finally the mystery is solved...

After further investigation, it turns out that the people reporting the problem were sharing the same adapters, which they failed to tell us here in Paris :mad:, hence the duplicate macs... :eek:

We now return you to your regularly scheduled programming...