---
upgrade:
  - |
    The libvirt driver port filtering feature will now ignore the ``use_ipv6``
    config option.

    The libvirt driver provides port filtering capability. This capability
    is enabled when the following is true:

    - The ``nova.virt.libvirt.firewall.IptablesFirewallDriver`` firewall driver
      is enabled
    - Security groups are disabled
    - Neutron port filtering is disabled/unsupported
    - An IPTables-compatible interface is used, e.g. an OVS VIF in hybrid mode,
      where the VIF is a tap device connected to OVS with a bridge

    When enabled, libvirt applies IPTables rules to all interface ports that
    provide MAC, IP, and ARP spoofing protection.

    Previously, setting the ``use_ipv6`` config option to ``False`` prevented
    the generation of IPv6 rules even when there were IPv6 subnets available.
    This was fine when using nova-network, where the same config option was
    used to control generation of these subnets. However, a mismatch between
    this nova option and equivalent IPv6 options in neutron would have resulted
    in IPv6 packets being dropped.

    Seeing as there was no apparent reason for not allowing IPv6 traffic when
    the network is IPv6-capable, we now ignore this option. Instead, we use the
    availability of IPv6-capable subnets as an indicator that IPv6 rules should
    be added.
