Neutron should disallow a CIDR of /32

[Paul Ward]

NeutronDbPluginV2._validate_allocation_pools() currently does basic checks to be sure you don't have an invalid subnet specified. However, one thing missing is checking for a CIDR of /32. Such a subnet would only have one valid IP in it, which would be consumed by the gateway, thus making this network a dead network since no IPs are left over to be allocated to VMs.

I propose a change to disallow start_ip == end_ip in NeutronDbPluginV2._validate_allocation_pools() to cover the CIDR of /32 case.

[Amir Sadoughi (amir-sadoughi)]

It is possible to have a subnet without a gateway. e.g. --no-gateway in neutronclient subnet-create.

[Paul Ward (wpward)]

Ok... is it useful to have a VM on a single IP subnet with no gateway though?

[Carl Baldwin (carl-baldwin)]

It isn't the job of the _validate_allocation_pools method to validate the subnet. Perhaps you are looking for a different validation method.

[Paul Ward (wpward)]

Thanks for your input, Carl. You're right, it seems the more appropriate place for this is _validate_subnet(). It checks ip version, gateway, etc... but not the size of the subnet.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/68742

[Paul Ward (wpward)]

It's been decided to abandon this fix because it's preventing something that, while not useful, is technically "ok". The better place for this fix would be in the UI as a hint to the user.

For more info: http://lists.openstack.org/pipermail/openstack-dev/2014-January/025385.html