A virtual network is implemented on a physical network. A virtual network data packet is tunneled through the physical network via encapsulation within a physical network data packet and via transmission of the physical network data packet through the physical network. A network congestion notification capability of the virtual network is preserved and modified during transmission of virtual network data through the physical network and vice-versa. Congestion notification metadata can be copied from a header of a virtual network data packet to a header of a physical network data packet when the virtual network data packet is encapsulated into the physical network data packet. Congestion notification metadata can be copied from a header of a physical network data packet to a header of a virtual network data packet when the virtual network data packet is decapsulated from the physical network data packet.