duplicaet MAC addresses (was: Re: how do I disable IPv6?)

[Gert Doering <gert%greenie.muc.de@localhost>]

Hi,

On Wed, Feb 28, 2018 at 01:52:16PM +0700, Robert Elz wrote:
>   | Although I've heard
>   | stories of duplicate MAC addresses from unscrupulous vendors before.
> 
> I have heard those stories as well, though never actually seen it,
> and I am not sure I have ever actually talked to anyone who had
> personally seen it either.

Just as a data point - I have :-) - small manufacturer of industrial PCs 
with onboard LAN cards.  One of the steps in the production line scanned 
MAC addresses from a printout with a barcode reader, programming them into 
the card EEPROMs.  One PC had the wrong line scanned, and two machines got 
the same MAC address, ending up both in the office network of said 
manufacturer.  Funny effects ensued...

(This is an anecdote, it happened 10+ years ago, and I assume it's not
happening very often)

Second anecdote: our vmware cloud managed to cough up a number of VMs with
the same MAC address.  Not sure exactly how that happened, but it was 
something about multiple clusters all doing dynamic MACs from the same
"base range", and then VMs getting moved from one cluster to the other,
keeping the MAC address.  The VMs didn't end up on the same network, but
a switch in-between did not have proper per-VLAN mac tables and funny
effects ensued...


So, yes, it happens.

gert
-- 
now what should I write here...

Gert Doering - Munich, Germany                             gert%greenie.muc.de@localhost