When upgrading an openVZ container from CentOS 7.0 to CentOS 7.1 a total loss of network connectivity may occur. The reason for this is that on startup of the network service the file /etc/sysconfig/network-scripts/iup-aliases performs the "arping" command to check if the main IP address is available for assignment on the network interface. Unfortunately, the return value of the command always reports the IP to be not available.

The following solution fixes this issue:

- Start your vServer in the Rescue System

- Open the File /OLD_SYSTEM/etc/sysconfig/network-scripts/ifup-aliases

- Look for the following line:

if [ "$setup_this" = "yes" ] ; then

- Replace the block of code following ths line with the following:

if [ "$setup_this" = "yes" ] ; then
if [ "${parent_device}" != "lo" ] &&  [ "${ARPCHECK}" != "no" ] && \
is_available ${parent_device} && \
( grep -qswi "up" /sys/class/net/${parent_device}/operstate ||  grep -qswi "1" /sys/class/net/${parent_device}/carrier ) ; then echo $"Determining if ip address ${IPADDR} is already in use for device ${parent_device}..."
/sbin/arping -q -c 2 -w ${ARPING_WAIT:-3} -D -I ${parent_device} ${IPADDR}
if [ $? = 1 ]; then
  net_log $"Error, some other host already uses address ${IPADDR}."
  return 1
fi
fi

- Disable the Rescue System and start the vServer in normal mode

- Network connectivity should now be given