A virtual network has network interfaces coupled by a multipoint tunnel (100) through a forwarding network (40), each interface having a forwarding address in an address space of the forwarding network, each network interface having a reconfigurable address mapper (320) for determining a forwarding address for a packet, and encapsulating the packet with its forwarding address so that the forwarding network can forward the data packet transparent to its destination address. This makes the virtual network more agile since changes to the virtual network can be achieved by reconfiguring the corresponding forwarding addresses without needing to set up new tunnels new routing to these different tunnels. The forwarding network need not be aware of the virtual network and so no adaptation of the forwarding network or specialised hardware is needed.