Neutron currently does not enforce the uniqueness, or non-overlap, of subnet cidrs within the address scope for a single tenant. For example, if a tenant chooses to use 10.0.0.0/24 on more than one subnet, he or she is free to do so. Problems will arise when trying to connect a router between these subnets but that is left up to the tenant to work out.
In the current IPAM rework, we had decided to allow this overlap in the reference implementation for backward compatibility. However, we've hit a snag. It would be convenient to use the subnet cidr as the handle with which to refer to a previously allocated subnet when talking to IPAM. If overlap is allowed, this is not possible and we need to come up with another identifier such as Neutron's subnet_id or another unique IPAM specific ID. It could be a burden on an external IPAM system -- which does not allow overlap -- to work with a completely separate identifier for a subnet. I do not know of anyone using this capability (or mis-feature) of Neutron. I would hope that tenants are aware of the issues with trying to route between subnets with overlapping address spaces and would avoid it. Is this potential overlap something that we should really be worried about? Could we just add the assumption that subnets do not overlap within a tenant's scope? An important thing to note is that this topic is different than allowing overlap of cidrs between tenants. Neutron will continue to allow overlap of addresses between tenants and support the isolation of these address spaces. The IPAM rework will support this. Carl Baldwin __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev