[openstack-dev] [neutron] Neutron should disallow /32 CIDR

Edgar Magana emagana at plumgrid.com
Tue Jan 21 21:04:47 UTC 2014

Wouldn't be easier just to check if:

cidr is 32?

 I believe it is a good idea to not allow /32 network but this is just my


From:  Paul Ward <wpward at us.ibm.com>
Reply-To:  OpenStack List <openstack-dev at lists.openstack.org>
Date:  Tuesday, January 21, 2014 12:35 PM
To:  OpenStack List <openstack-dev at lists.openstack.org>
Subject:  [openstack-dev] [neutron] Neutron should disallow /32 CIDR

Currently, NeutronDbPluginV2._validate_allocation_pools() does some very
basic checking to be sure the specified subnet is valid.  One thing that's
missing is checking for a CIDR of /32.  A subnet with one IP address in it
is unusable as the sole IP address will be allocated to the gateway, and
thus no IPs are left over to be allocated to VMs.

The fix for this is simple.  In
NeutronDbPluginV2._validate_allocation_pools(), we'd check for start_ip ==
end_ip and raise an exception if that's true.

I've opened lauchpad bug report 1271311
(https://bugs.launchpad.net/neutron/+bug/1271311) for this, but wanted to
start a discussion here to see if others find this enhancement to be a
valuable addition.
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