Re: DAD question

[[e-mail]]

> > it may be a fair assumption that if an address based on the MAC address is duplicate, the MAC address itself is a duplicate.
> 
> True, but the odds of this happening are very low.  I wonder if we have any data on DAD detecting duplicate addresses and their cause.

You may need to qualify "very low".

> For example, has any seen any actual duplicate MAC addresses?  It would be good to collect some data.

Duplicate MAC addresses are regularly seen in the wild. As an example,
from a nearby DHCP server, I have the following duplicates from a total
of 65499 MAC addresses:

5 00:90:4c:91:00:01;
3 00:40:10:20:00:02;
3 00:00:00:00:00:00;
2 bc:b1:f3:61:28:e3;
2 98:0c:82:84:ef:83;
2 34:21:09:03:76:f9;
2 00:1f:1f:8c:d4:d5;
2 00:1f:1f:8c:d4:cd;
2 00:1d:73:11:11:13;
2 00:11:22:33:44:56;

So from this sample a total of 10 MAC addresses occur more than once
(different customers, different locations).

I make no claims about these numbers being representative. My main 
point is that duplicates *occur*, for several different reasons, e.g.

- Manufacturing mistakes
- Software bugs
- MAC address explicitly set

Steinar Haug, Nethelp consulting, [e-mail]