One of the most interesting new features in Neutron for the Kilo release is the addition of subnetpools to the API. This work was initially targeted to integrate nicely with pluggable IPAM. Unfortunately, this did not make it into Kilo and is targeted at Liberty. But even without pluggable IPAM as a consumer, the subnetpools addition is quite useful. Here’s an example of how you might use it.

neutron net-create webapp
neutron subnetpool-create –default-prefixlen 24 –pool-prefix webpool
neutron subnet-create –subnetpool webpool websubnet

What I’ve shown above is the creation of a network, pool, and subnet for an example web application. The subnetpool was created with a default prefix length of /24. Thus, when the user creates the subnet ‘websubnet’, it will end up with a CIDR such as “”.

Creating another subnet from the pool will result in the allocation code selecting another range:

neutron subnet-create –subnetpool webpool dbsubnet

This would result in the subnet ‘dbsubnet’ having a CIDR of “”.

As you can see, the subnetpool code is really powerful because it removes the need for a user to have to select a CIDR. An admin could create a shared subnetpool with a large block of addresses and let tenants create subnets from that. It’s a powerful addition to the Neutron API, and will integrate nicely with the pluggable IPAM addition we expect to land during Liberty.