Virtual computing instances are provisioned with network resource allocation constraints, which may include hard constraints that must be met in order for the virtual computing instances to be created in a host server. Network resources from multiple hosts may be pooled in a virtual switch, and a cloud management system (CMS) may ensure that a network bandwidth reservation for a new virtual computing instance can be accommodated by network bandwidth in the pool that is reserved for communication endpoint traffic. In addition to such CMS-level constraint enforcement, techniques disclosed herein may also enforce network bandwidths constraints at the host level to guarantee that network bandwidth reservation requirements for communication endpoint(s) of a new virtual computing instance can be satisfied by a particular host before creating the virtual computing instance in that host.