[CentOS] Strange XEN on CentOS HWaddr Address Issue

Sergey Smirnov sergey.a.smirnov at gmail.com
Tue Aug 4 13:14:48 UTC 2009


This commonly happens when you using Xen in the bridged mode (when you
reboot your system the first time, this is default Xen configuration).
You have to change your configuration to routed mode if you want to
prevent that in future.

You can get more info about network in Xen going by links below -


P.S. my first experience with Xen starting from the same issue like
your (is was a problem for me, because I have dedicated server and
support stuff from hosting company every time when the NIC address was
changed want to kick me)... :)

On Tue, Aug 4, 2009 at 4:43 PM, Brett Serkez<bserkez at gmail.com> wrote:
> 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,
> Brett
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Sergey Smirnov
Moscow, Russia GMT+3
cell phone: +7 919 104 8963
email/xmpp: Sergey.A.Smirnov at Gmail.com

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