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[wujun <wujun@xxxxxxxxxxx>]

** Changed in: neutron
       Status: Invalid => Confirmed

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https://bugs.launchpad.net/bugs/1580927

Title:
  spans beyond the subnet for /31 and /32 in IPam

Status in neutron:
  Confirmed

Bug description:
  summary:  When needing to create a point to point connection via a
  subnet, generally and /31 is the recommended cidr.  Neutron supports
  /31 via disabling dhcp and gateway on a subnet.   However, IPam does
  not provide the allocation pool of the subnet properly and a VM cannot
  be created.

  Steps to reproduce

  root@ubuntu:~# neutron subnet-create  --disable-dhcp --no-gateway --cidr=10.14.0.20/31 --name bug-subnet 69c5342a-5526-4257-880a-f8fd2e633de9
  Created a new subnet:
  +-------------------+--------------------------------------+
  | Field             | Value                                |
  +-------------------+--------------------------------------+
  | allocation_pools  |                                      |
  | cidr              | 10.14.0.20/31                        |
  | dns_nameservers   |                                      |
  | enable_dhcp       | False                                |
  | gateway_ip        |                                      |
  | host_routes       |                                      |
  | id                | 63ce4e26-9838-4fa3-b2d5-e59f88f5b7ce |
  | ip_version        | 4                                    |
  | ipv6_address_mode |                                      |
  | ipv6_ra_mode      |                                      |
  | name              | bug-subnet                           |
  | network_id        | 69c5342a-5526-4257-880a-f8fd2e633de9 |
  | subnetpool_id     |                                      |
  | tenant_id         | ca02fc470acc4a27b468dff32ee850b2     |
  +-------------------+--------------------------------------+
  root@ubuntu:~# neutron subnet-update --allocation-pool start=10.14.0.20,end=10.14.0.21 bug-subnet
  The allocation pool 10.14.0.20-10.14.0.21 spans beyond the subnet cidr 10.14.0.20/31.

  Recommended Fix:

  in db/ipam_backend_mixin.py :: function: validate_allocation_pools
  ~~lines: 276

             if start_ip < subnet_first_ip or end_ip > subnet_last_ip:
                  LOG.info(_LI("Found pool larger than subnet "
                               "CIDR:%(start)s - %(end)s"),
                           {'start': start_ip, 'end': end_ip})
                  raise n_exc.OutOfBoundsAllocationPool(
                      pool=ip_pool,
                      subnet_cidr=subnet_cidr)

  This if block should have a special case for ipv4 /31 and /32  for "<= and >=" :   
                  start_ip <= subnet_first_ip or end_ip >= subnet_last_ip

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