Comment 0 for bug 2040242

As we know, we can use ipv6 address end with '0' like 2001::.

But when we allocate ipv6 pool use neutron, we could find the error like follows:
neutron net-create net-v6
neutron subnet-create --ip-version 6 --allocation-pool start=2001::,end=2001::2 net-v6 2001::/64
The allocation pool 2001::-2001::2 spans beyond the subnet cidr 2001::/64.
Neutron server returns request_ids: ['req-9a6569ed-52d7-4c3f-ad7e-8986a041a347']

We found that the error info from the func 'validate_allocation_pools':

        else: # IPv6 case
            subnet_first_ip = netaddr.IPAddress(subnet.first + 1)
            subnet_last_ip = netaddr.IPAddress(subnet.last)

        LOG.debug("Performing IP validity checks on allocation pools")
        ip_sets = []
        for ip_pool in ip_pools:
            start_ip = netaddr.IPAddress(ip_pool.first, ip_pool.version)
            end_ip = netaddr.IPAddress(ip_pool.last, ip_pool.version)
            if (start_ip.version != subnet.version or
                    end_ip.version != subnet.version):
                LOG.info("Specified IP addresses do not match "
                         "the subnet IP version")
                raise exc.InvalidAllocationPool(pool=ip_pool)
            if start_ip < subnet_first_ip or end_ip > subnet_last_ip:
                LOG.info("Found pool larger than subnet "
                         "CIDR:%(start)s - %(end)s",
                         {'start': start_ip, 'end': end_ip})
                raise exc.OutOfBoundsAllocationPool(
                    pool=ip_pool,
                    subnet_cidr=subnet_cidr)

Why neutron ipam force first ip of one pool < (subnet.first + 1) if version of subnet is ipv6 ?