Winner of Best Paper at LISA 09. Describes project Crossbow in OpenSolaris, which is introducing new abstractions that provide virtual network interface cards (VNICs) and virtual switches that can have dedicated hardware resources and bandwidth assigned to them. Multiple VNICs can be assigned to OpenSolaris zones to create virtual network machines (VNM) that provide higher level networking functionality like virtual routing, virtual load balancing, and so on. These components can be combined to build an arbitrarily complex virtual network called virtual wire (vWire) which can span one or more physical machines. vWires on the same physical network can be VLAN-separated and support dynamic migration of virtual machines, which is an essential feature for hosting and cloud operators.