[CentOS] the wandering MAC?

Wed Oct 13 16:28:27 UTC 2010
Boris Epstein <borepstein at gmail.com>

Hi all,

I have what appears to be a truly puzzling problem. I've got this P4
32-bit machine running CentOS 5.5 with XEN that has two NICs: one
onboard, an Intel Corporation 82540EM Gigabit and one on an expansion
card, Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit. The second one
is recognized as eth1.

What's happening is, it is showing up under one of the two MAC's:
either 00:0a:cd:1a:c1:71 or 00:00:00:00:c1:71. If you reboot it the
MAC stays the same; if you shutdown and do a full powerdown it seems
to change.

Obviously, after it goes from one MAC to another you have to play with
the start-up scripts for this interface to start up correctly and this
becomes a major annoyance.

Any idea what all of this mess could mean?