Attaching intances to network that do have a subnet

Issue

• We need clarification about the possibility to attach an instance to a network that does not have a subnet. It seams that in the PWG environment subnets are not necessary: OpenStack does not control ip ranges, does not provide dhcp, gateway and host routes. There is also no need for security groups. Because OpenStack does not know what IP address will be assigned to the instance, it cannot insert any valid iptables rules; so security groups do not have any sense. The problem is if we create a provider network (of any type) with no subnets and try to boot an instance attached to this network, nova returns an error because it tries to configure default security group on the port and the network does not support such operation.