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[Alan Pevec <1447883@xxxxxxxxxxxxxxxxxx>]

** Also affects: neutron/icehouse
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1447883

Title:
  Restrict netmask of CIDR to avoid DHCP resync is not enough

Status in OpenStack Neutron (virtual network service):
  Fix Committed
Status in neutron icehouse series:
  Fix Committed
Status in neutron kilo series:
  Fix Released
Status in OpenStack Security Advisories:
  Won't Fix

Bug description:
  Restrict netmask of CIDR to avoid DHCP resync  is not enough.
  https://bugs.launchpad.net/neutron/+bug/1443798

  I'd like to prevent following case:

  [Condition]
    - Plugin: ML2
    - subnet with "enable_dhcp" is True

  [Operations]
  A. Specify "[]"(empty list) at "allocation_pools" when create/update-subnet
  ---------------------------------------------------------------------------
  $ $ curl -X POST -d '{"subnet": {"name": "test_subnet", "cidr": "192.168.200.0/24", "ip_version": 4, "network_id": "649c5531-338e-42b5-a2d1-4d49140deb02", "allocation_pools": []}}' -H "x-auth-token:$TOKEN" -H "content-type:application/json" http://127.0.0.1:9696/v2.0/subnets

  Then, the dhcp-agent creates own DHCP-port, it is reproduced resync
  bug.

  B. Create port and exhaust allocation_pools
  ---------------------------------------------------------------
  1. Create subnet with 192.168.1.0/24. And, DHCP-port has alteady created.
     gateway_ip: 192.168.1.1
     DHCP-port: 192.168.1.2
     allocation_pools{"start": 192.168.1.2, "end": 192.168.1.254}
     the number of availability ip_addresses is 252.

  2. Create non-dhcp port and exhaust ip_addresses in allocation_pools
     In this case, user creates a port 252 times.
     the number of availability ip_addresses is 0.

  3. User deletes the DHCP-port(192.168.1.2)
     the number of availability ip_addresses is 1.

  4. User creates a non-dhcp port.
     the number of availability ports are 0.
     Then, dhcp-agent tries to create DHCP-port. It is reproduced resync bug.

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