Comment 4 for bug 975043

Reviewed: https://review.openstack.org/6832
Committed: http://github.com/openstack/nova/commit/7c64de95f422add711bcdf5821310435e7be0199
Submitter: Jenkins
Branch: stable/essex

commit 7c64de95f422add711bcdf5821310435e7be0199
Author: Cor Cornelisse <email address hidden>
Date: Fri Apr 6 15:54:16 2012 +0200

    Cloudpipe tap vpn not always working

    Fixes bug 975043

    Since Essex, all instances will have an eth0 MAC address in the range
    of FA:16:3E, which is near the end of the MAC address space.

    When openvpn is started, a TAP interface is created with a random
    generated MAC address. Chances are high the generated MAC address is
    lower in value than the eth0 MAC address. Once the tap interface is
    added to the bridge interface, the bridge interface will no longer have
    the eth0 MAC address, but take over the TAP MAC address. This is a
    feature of the linux kernel, whereby a bridge interface will take the
    MAC address with the lowest value amongst its interfaces. After the ARP
    entries expire, this will result in the cloudpipe instance being no
    longer reachable.

    This fix, randomly generates a MAC address starting with FA:17:3E, which
    is greater than FA, and will thus ensure the brige will keep the eth0 MAC
    address.

    Change-Id: I0bd994b6dc7a92738ed23cd62ee42a021fd394e2