---
fixes:
  - |
    The Neutron API has been changed to validate network MTU minimums.
    A network's MTU is now only valid if it is the minimum value
    allowed based on the IP version of the associated subnets,
    68 for IPv4 and 1280 for IPv6.

    This minimum is now enforced in the following ways:

    * When a subnet is associated with a network, validate
      the MTU is large enough for the IP version. Not only
      would the subnet be unusable if it was allowed, but the
      Linux kernel can fail adding addresses and configuring
      network settings like the MTU.

    * When a network MTU is changed, validate the MTU is large
      enough for any currently associated subnets. Allowing a
      smaller MTU would render any existing subnets unusable.

    See bug `1988069 <https://bugs.launchpad.net/neutron/+bug/1988069>`_
    for more information.
