Comment 6 for bug 1844349

Reviewed: https://review.opendev.org/699189
Committed: https://git.openstack.org/cgit/openstack/kolla-ansible/commit/?id=eeff8e011a70bf1cef15c7db281d3d2c5f9ad6f4
Submitter: Zuul
Branch: stable/train

commit eeff8e011a70bf1cef15c7db281d3d2c5f9ad6f4
Author: Pierre Riteau <email address hidden>
Date: Wed Nov 27 16:32:47 2019 +0100

    [neutron] Adjust neighbour table thresholds

    When clouds have a large number of hosts, the default size of the ARP
    cache is too small. The cache can overflow, which means that the system
    has no way to reach some IP addresses.

    Increasing threshold limits addresses the situation, in a reasonably
    safe way (the maximum impact is 5MB or so of additional RAM used).

    More context on this issue:

    * http://man7.org/linux/man-pages/man7/arp.7.html
    * https://bugs.launchpad.net/charm-nova-compute/+bug/1780348
    * https://bugs.launchpad.net/fuel/+bug/1488938
    * https://bugs.launchpad.net/tripleo/+bug/1690087
    * https://github.com/crowbar/crowbar-openstack/commit/0583a0c94996df6b784229e8a534f955eaca85bc
    * https://github.com/crowbar/crowbar-openstack/commit/3dd21ea62ac152e40bfdfee4b8e25a528c82a79f
    * https://opendev.org/openstack/tripleo-heat-templates/commit/1651a1805a16212299fe0a91aebb2a91ed39bc6e

    Change-Id: I60c871e8eb9f2c086818ff077987f2390930800c
    Closes-Bug: #1844349
    (cherry picked from commit 4234cc4b5b3ca7172c9d184ed3f145b955f11163)