Comment 3 for bug 2040242

OK,
If we create one subnet with CIDR 2003::/64 without a gateway, the response body looks like the following:

neutron subnet-create --no-gateway --ip-version 6 net_v6 2003::/64
+-------------------+----------------------------------------------------------+
| Field | Value |
+-------------------+----------------------------------------------------------+
| allocation_pools | {"start": "2003::1", "end": "2003::ffff:ffff:ffff:ffff"} |
| cidr | 2003::/64 |
| created_at | 2023-10-27T03:17:51Z |
| description | |
| dns_nameservers | |
| enable_dhcp | True |
| gateway_ip | |
| host_routes | |
| id | c27ab9cf-92fb-401c-a9c9-e8a1a7d42f5f |
| ip_version | 6 |
| ipv6_address_mode | |
| ipv6_ra_mode | |
| name | |
| network_id | 4c5da8a5-ab7a-4937-a943-6a4c0413922e |
| project_id | 8eae7e2bedcd4df5bf96a895240f148b |
| revision_number | 0 |
| service_types | |
| subnetpool_id | |
| tags | |
| tenant_id | 8eae7e2bedcd4df5bf96a895240f148b |
| updated_at | 2023-10-27T03:17:51Z |
+-------------------+----------------------------------------------------------+

We found that the allocation_pools do not contain '2003::'. Why does IPAM delete the first IP of the CIDR?