Normal?  No, this goes against a lot of things networking, so definitely 
not kosher.  Two mac's in a broadcast domain is an extremely bad thing 
usually causing a switch to start flooding unicast traffic within a 
vlan.  Microsoft thought this was a great way to do redundancy with 
Network Load-Balancing replicating macs among cluster members until 
network people realized it was breaking their lans (essentially turning 
switches into hubs).  I have some mega-outages I can attribute to this 
commonly over the years...

Does it happen?  Sure - as chinese companies clone each other and other 
legit vendor hardware apparently eeprom data and all, not bothering to 
register an oui id themselves, I'm not entirely surprised.  Buy those $5 
ebay generic nics in bulk, i'm sure you'll start getting mac collisions.

Another reason to stay with reputable sources of hardware...

I'd be curious what hardware it is being cloned indiscriminately, as 
would whoever owned the rights to the registered OUI.

https://www.wireshark.org/tools/oui-lookup.html

-mb


On 02/06/2014 04:50 PM, Daniel Stasinski wrote:
> The past few days I've been trying to solve a mystery.
>
> I've run a disability chat room for 17 years now and the whole time we
> have had our own custom chat client that connects to a customized
> ircd.  For the identd portion of the connect, I have always used an 8
> digit random number but as of v3 of the client, I seeded the random
> number generator with their MAC address so their identd would be the
> same if they re-installed.  I have always been under the impression
> that no two devices would ever share the same MAC.  Note that this
> isn't a security issue for the site, it's just a convenience thing for
> me.
>
> In the last couple of months, 4 people have come in with duplicate
> id's.  This has never happened before.  Finally today a new guy came
> in and he turned out to be a programmer too so we talked about it and
> he gave me his pc's mac address.  58-2c-80-13-92-63. On a whim, I
> googled it and holy crap!
>
> I'm going to switch algorithms but I'm still curious, is it normal for
> vendors to recycle MAC addresses?
>
> Daniel
>