Comment 4 for bug 1521666

Reviewed: https://review.openstack.org/301747
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=2aa23de58f55f7b1001508326c5ac2627ba3a429
Submitter: Jenkins
Branch: master

commit 2aa23de58f55f7b1001508326c5ac2627ba3a429
Author: Sergey Nechaev <email address hidden>
Date: Tue Apr 5 14:40:59 2016 +0000

    Adding support of releasing DHCPv6 leases

    Original problem is that dhcp_release does not work with IPv6, but IPv6
    leases still should be released. For example:

    1. Start VM in dhcpv6-stateful network, make it acquire IPv6 address.
    2. Delete VM.
    3. Start another VM in same network before lease expires.

    There's a very high chance that the same IPv6 address will be allocated
    for both of these VMs (same address will be reused after first VM was
    deleted).

    On DHCP agent, hosts file would be changed, but not lease file, so
    dnsmasq will not give second VM address until lease expires. Reducing
    lease time is not a good solution here.

    Solution is adding invocation of dhcp_release6 utility when
    releasing IPv6 address. dhcp_release6 utility appears in dnsmasq 2.76.
    It crafts DHCP6_Release packet, sends it from passed network
    interface to IPv6 multicast address and waits for DHCP6_Reply.

    Closes-Bug: 1521666
    Change-Id: I5efab81cdaf0676503b6c7da0d4b4f400d859286