Comment 1 for bug 1615351

Problem is with DHCP port.

When creating subnet _handle_create_subnet_dhcp() function
returns DHCP address as a string and does not create a new port.

   def _handle_create_subnet_dhcp(self, context, subnet):
        """Create the dhcp configration for the subnet

        Returns the dhcp server port if configured
        """
        if subnet['enable_dhcp']:
            if cfg.CONF.df.use_centralized_ipv6_DHCP:
              return subnet['allocation_pools'][0]['start']

The last command returns IP in ipv4 format.