I just create an Oracle Enterprise Linux virtual machine on a Xen Server, and this weird thing happened. I tried to assign a private address (172.16.195.4) and this error message appears: Error message: Some other host already uses address 172.16.195.4
I decided to make an arping as follows:
arping -I eth0 -c 3 172.16.195.4
..and the resulting MAC address belongs to our main router (a Cisco 2900).
So, the thing is, no matter which (private) IP I use as an argument in the previous command, the answer is the same MAC, and the error appears every time I try to setup ANY IP address on the Linux Box.
When I use a public IP address, it throws no error whatsoever.
Not really, the virtual machine has only one virtual NIC, which has a 1:1 relationship with the hardware NIC. The server has 8 NICs, but only those used in the VMs are physically connected to the switch.
Turns out in the end that in fact our router was grabbing all the private IPs because of some NAT configuration that is needed to communicate with our main office. It seems that if we setup the same IP, but in a different VLAN, it will also work with the proper configuration of our switch.