A switch in a network of interconnected switches (101, 102, 103, 104, 105), wherein the switch comprises: a network extension module adapted to: maintain a mapping between a first virtual local area network (VLAN) identifier (112, 114, 116) used by a tenant and a first global VLAN identifier of a network extension group, wherein the network extension group is represented by a range of global VLAN identifiers for the tenant, said range including one aggregate global VLAN identifier and multiple edge global VLAN identifiers (142, 144); and include the first global VLAN identifier in a packet belonging to the first VLAN; wherein a global VLAN identifier is persistent in a respective switch of the network and represents a virtual forwarding domain in the network; and wherein the switch is an aggregate switch for one or more edge switches (103, 104, 105) and the first global VLAN identifier is the aggregate global VLAN identifier of the network extension group, and wherein the aggregate global VLAN identifier is mapped to all VLANs of the respective tenant for the network extension group, comprising the aggregate switch adapted to maintain: an internal identifier mapping to map one or more fields of a header of the packet comprising information of the respective tenant to a respective internal identifier; a global VLAN mapping to map the respective internal identifier to the aggregate global VLAN identifier; wherein the aggregate global VLAN identifier of the network extension group is represented using combined bits dedicated for both a tenant VLAN identifier and an additional VLAN identifier in a flat representation. a network extension module adapted to: maintain a mapping between a first virtual local area network (VLAN) identifier (112, 114, 116) used by a tenant and a first global VLAN identifier of a network extension group, wherein the network extension group is represented by a range of global VLAN identifiers for the tenant, said range including one aggregate global VLAN identifier and multiple edge global VLAN identifiers (142, 144); and include the first global VLAN identifier in a packet belonging to the first VLAN; wherein a global VLAN identifier is persistent in a respective switch of the network and represents a virtual forwarding domain in the network; maintain a mapping between a first virtual local area network (VLAN) identifier (112, 114, 116) used by a tenant and a first global VLAN identifier of a network extension group, wherein the network extension group is represented by a range of global VLAN identifiers for the tenant, said range including one aggregate global VLAN identifier and multiple edge global VLAN identifiers (142, 144); and include the first global VLAN identifier in a packet belonging to the first VLAN; wherein a global VLAN identifier is persistent in a respective switch of the network and represents a virtual forwarding domain in the network; and wherein the switch is an aggregate switch for one or more edge switches (103, 104, 105) and the first global VLAN identifier is the aggregate global VLAN identifier of the network extension group, and wherein the aggregate global VLAN identifier is mapped to all VLANs of the respective tenant for the network extension group, comprising the aggregate switch adapted to maintain: an internal identifier mapping to map one or more fields of a header of the packet comprising information of the respective tenant to a respective internal identifier; a global VLAN mapping to map the respective internal identifier to the aggregate global VLAN identifier; wherein the aggregate global VLAN identifier of the network extension group is represented using combined bits dedicated for both a tenant VLAN identifier and an additional VLAN identifier in a flat representation. an internal identifier mapping to map one or more fields of a header of the packet comprising information of the respective tenant to a respective internal identifier; a global VLAN mapping to map the respective internal identifier to the aggregate global VLAN identifier; wherein the aggregate global VLAN identifier of the network extension group is represented using combined bits dedicated for both a tenant VLAN identifier and an additional VLAN identifier in a flat representation.