The tale of a single MAC

Adrian Chadd adrian at
Sat Jan 1 22:13:43 CST 2011

So along simlar lines, Ubiquiti sell routerstation pro boards with
sequential MAC addresses.

The trouble is they've allocated a single MAC for the first port - the
second ethernet port (also attached to the bridge) doesn't get a second

So in a purchase of a few hundred boards, we had plenty that were sequential.
Since the FreeBSD driver allocated MAC+1 to the second NIC, this caused
duplcate MAC addresses and this caused hilarity to ensue.

The "fix" was to just get this company to apply for some MAC space and then
use -that- on the second NIC and the bridge interfaces.

Ah, vendors.. :-)


On Sat, Jan 01, 2011, Graham Wooden wrote:
> Hi there,
> I encountered an interesting issue today and I found it so bizarre ? so I
> thought I would share it.
> I brought online a spare server to help offload some of the recent VMs that
> I have been deploying.  Around the same time this new machine (we?ll call it
> Server-B) came online, another machine which has been online for about a
> year now stopped responding to our monitoring (and we?ll name this
> Server-A). I logged into the switch and saw that the machine that stopped
> responding was in the same VLAN as this newly deployed, and then quickly
> noticed that Server-A?s MAC address was now on Server-B?s switch port.
> ?What the ...? was my initial response.
> I went ahead and moved Server-B?s to another VLAN, updated the switchport,
> cleared the ARP, and Server-A came back to life.  Happy new year to me.
> So ? here is the interesting part... Both servers are HP Proliant DL380 G4s,
> and both of their NIC1 and NIC2 MACs addresses are exactly the same.  Not
> spoofd and the OS drivers are not mucking with them ... They?re burned-in ?
> I triple checked them in their respective BIOS screen.  I acquired these two
> machines at different times and both were from the grey market.  The ?What
> the ...? is sitting fresh in my mind ...  How can this be?
> In the last 15 years of being in IT, I have never encountered a ?burned-in?
> duplicated MACs across two physically different machines.  What are the
> odds, that HP would dup?d them and that both would eventually end up at my
> shop?  Or maybe this type of thing isn?t big of deal... ?
> -graham

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