neutron/releasenotes/notes/sending-garp-for-l3-ha-c118...

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issues:
- In kernels < 3.19 ``net.ipv4.ip_nonlocal_bind`` sysctl option was not
isolated to network namespace scope. L3 HA sets this option to zero to
avoid sending gratuitous ARPs for IP addresses that were removed while
processing. If this happens, then gratuitous ARPs will be sent. It may
populate ARP cache tables of peer machines with wrong MAC addresses.
fixes:
- Versions of ``keepalived`` < 1.2.20 don't send gratuitous ARPs when
keepalived process receives a ``SIGHUP`` signal. These versions are not
packaged in some Linux distributions like Red Hat Enterprise Linux 7,
CentOS 7, or Ubuntu Xenial. Not sending gratuitous ARPs may lead to peer
ARP cache tables containing wrong entries about floating IP addresses until
those entries are invalidated. To fix that scenario, Neutron now sends
gratuitous ARPs for all new IP addresses that appear on non-HA interfaces
in router namespaces. This behavior simulates behavior of new versions of
``keepalived``.