[CentOS] Strange XEN on CentOS HWaddr Address Issue

Brett Serkez bserkez at gmail.com
Tue Aug 4 17:30:51 UTC 2009

> Maybe because you are looking at the bridge's mac and not the
> ethernet's which would be peth0.

No I am not.  dmesg shows the kernel messages at boot and it is
looking at the physical device, let's not get distracted, the issue is
clear in this regard.  As I previously stated, this happens even when
uninstalling XEN and booting off the non-XEN kernel since the install
of XEN.

> indeed, AFAIK all hardware adapters start with 00. This must have been set
> in the BIOS or with a boot option or in the network config.

This was helpful, gave me places/incentive to continue looking.

In /etc/sysconfig/network-scripts/ifcfg-eth1 I found:

# Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit Ethernet

So now I know what the original MAC address was.

Here is where it gets interesting.  The following file was modified at
the date/time that the XEN kernel was first booted:


and it has fe:ff:ff:ff:ff:ff  for BOTH network adapters:

desc: "Realtek Semiconductor Co., Ltd. RTL-8169 Gigabit Ethernet"
networfe:ffddr: fe:ff:ff:ff:ff:ff
vendorId: 10ec
deviceId: 8169
subVendorId: 10ec
subDeviceId: 8169
pciType: 10

desc: "Intel Corporation 82562EZ 10/100 Ethernet Controller"
network.hwaddr: fe:ff:ff:ff:ff:ff
vendorId: 8086
deviceId: 1050
subVendorId: 8086
subDeviceId: 303a

Everything I'm finding is re-enforcing my original theory that XEN
modified the hwaddr of this NIC.

The question continues to be what caused this and how to change it
back.  Given this is a stock system, I have to believe others must
have/may run into this issue.


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