One embodiment of the present invention provides a switch in a network of interconnected switches. The switch includes a network extension module, which maintains a mapping between a first virtual local area network (VLAN) identifier and a first global VLAN identifier of a network extension group. The network extension group is represented by a range of global VLAN identifiers for a tenant. A global VLAN identifier is persistent in a respective switch of the network and represents a virtual forwarding domain in the network. During operation, the network extension module includes the global VLAN identifier in a packet belonging to the first VLAN.