Comment 8 for bug 1608400

Reviewed: https://review.openstack.org/554729
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=34b7213ee37d80ef1844f0bf8baae3fca1535038
Submitter: Zuul
Branch: stable/pike

commit 34b7213ee37d80ef1844f0bf8baae3fca1535038
Author: Swaminathan Vasudevan <email address hidden>
Date: Wed Mar 7 19:03:42 2018 -0800

    DVR: Fix allowed_address_pair IP, ARP table update by neutron agent

    Allowed_address_pair IP when associated with a network port will
    inherit the services MAC.
    Right now the ARP entry is updated with the last MAC that it is
    associated with. But when allowed_address_pair IPs are used in
    the context of VRRP the MAC keeps switching between the MASTER
    and SLAVE. VRRP instance sends out GARP, but the ARP entry in the
    router namespace is not getting updated based on the GARP.

    This might cause the VRRP IP and the service using the IP to fail.

    Since we having been adding the ARP entry with NUD state as
    PERMANENT, the ARP entries are set for ever and does not adopt the
    GARP sent out by the VRRP instance.

    This will cause instances associated with DVR routers to have a
    service interruption.

    So the proposed patch will add the ARP entry for the Allowed address
    pair with NUD for 'REACHABLE'.
    This allows the Allowed_address_pair IP MAC to be updated on the
    fly.

    Change-Id: I43c3471f5d259e8c2ee1685398a06a4680c0bfcd
    Closes-Bug: #1608400
    (cherry-picked from commit fbe308bdc12191c187343b5ef103dea9af738380)