[CentOS] Strange XEN on CentOS HWaddr Address Issue

Brett Serkez bserkez at gmail.com
Tue Aug 4 12:43:28 UTC 2009

Ran into a strange issue with XEN on CentOS that I think is specific
to CentOS, which is why I'm starting by posting to this list first,
I'll post on the XEN list depending on responses.  My sense is this
issue has something to do with how CentOS handles network setup on
first boot of the XEN kernel.

- Installed a brand new CentOS 5.3 server with minimal packages.

- Installed XEN, modified grub.conf to boot off of the XEN kernel and rebooted.

- After reboot, network connectivity was lost.

- Investigation concluded the issue was that the HWaddr address of the
physical NIC matched the fabricated HWaddr that XEN uses for most of
its adapters:  FE:FF:FF:FF:FF:FF.

 - Temporary resolution, I re-enabled the motherboard's NIC, rebooted,
all seems to be working.

I would like to get the NIC in question working as it is a GigaBit
NIC, but it still has the HWaddr:  FE:FF:FF:FF:FF:FF which conflicts
with XEN.

My understanding of the HWaddr is that the first portion is
manufacturer assigned for uniqueness, I cannot image this NIC
originally had this HWaddr, but I don't know what it originally was.

Does anyone know if this value is read from the NIC on each boot, or
is it stored in a file after the first boot?  Is there someway to undo
this change so the NIC returns to its original value or atleast a
non-conflicting value?

Has anyone else seen this behavior?

Thank you in advance,


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