A computer-implemented method, comprising: in a first enclave of a label switching network, formatting, by one or more computing devices, a protocol data unit, PDU, of the label switching network to include a network service field specifying at least one network service to be applied to the PDU, wherein the PDU specifies routing and forwarding information of the PDU for a path in the label switching network ending in an enclave of the label switching network other than the first enclave, and routing and forwarding information between enclaves in a non-label switching network; communicating, by the one or more computing devices, the formatted PDU from the first enclave, via the non-label switching network, to a second enclave of the label switching network in accordance with the routing and forwarding information between enclaves in the non-label switching network; in the second enclave of the label switching network: determining, by one or more computing devices, from the network service field of the communicated PDU, each network service specified to be applied to the PDU in the second enclave; applying, by the one or more computing devices, each of the determined network services to the PDU; and transmitting, by the one or more computing devices, the network-serviced PDU in accordance with the routing and forwarding information of the PDU in the label switching network, wherein the non-label switching network is an Internet Protocol, IP, network, and wherein the network service field describes network service chaining, wherein the label switching network is a MultiProtocol Label Switching, MPLS, network, and wherein the network service field is formatted as a network service header, NSH), wherein formatting comprises: formatting a generic routing encapsulation, GRE, field of the non-label switching network ahead of the NSH field; and formatting an MPLS label of the MPLS VPN as a context header in the NSH field, or formatting a generic routing encapsulation, GRE, field of the non-label switching network, including an MPLS label of the MPLS VPN, ahead of the NSH field. in a first enclave of a label switching network, formatting, by one or more computing devices, a protocol data unit, PDU, of the label switching network to include a network service field specifying at least one network service to be applied to the PDU, wherein the PDU specifies routing and forwarding information of the PDU for a path in the label switching network ending in an enclave of the label switching network other than the first enclave, and routing and forwarding information between enclaves in a non-label switching network; communicating, by the one or more computing devices, the formatted PDU from the first enclave, via the non-label switching network, to a second enclave of the label switching network in accordance with the routing and forwarding information between enclaves in the non-label switching network; in the second enclave of the label switching network: determining, by one or more computing devices, from the network service field of the communicated PDU, each network service specified to be applied to the PDU in the second enclave; applying, by the one or more computing devices, each of the determined network services to the PDU; and transmitting, by the one or more computing devices, the network-serviced PDU in accordance with the routing and forwarding information of the PDU in the label switching network, wherein the non-label switching network is an Internet Protocol, IP, network, and wherein the network service field describes network service chaining, wherein the label switching network is a MultiProtocol Label Switching, MPLS, network, and wherein the network service field is formatted as a network service header, NSH), wherein formatting comprises: formatting a generic routing encapsulation, GRE, field of the non-label switching network ahead of the NSH field; and formatting an MPLS label of the MPLS VPN as a context header in the NSH field, or formatting a generic routing encapsulation, GRE, field of the non-label switching network, including an MPLS label of the MPLS VPN, ahead of the NSH field. determining, by one or more computing devices, from the network service field of the communicated PDU, each network service specified to be applied to the PDU in the second enclave; applying, by the one or more computing devices, each of the determined network services to the PDU; and transmitting, by the one or more computing devices, the network-serviced PDU in accordance with the routing and forwarding information of the PDU in the label switching network, wherein the non-label switching network is an Internet Protocol, IP, network, and wherein the network service field describes network service chaining, wherein the label switching network is a MultiProtocol Label Switching, MPLS, network, and wherein the network service field is formatted as a network service header, NSH), wherein formatting comprises: formatting a generic routing encapsulation, GRE, field of the non-label switching network ahead of the NSH field; and formatting an MPLS label of the MPLS VPN as a context header in the NSH field, or formatting a generic routing encapsulation, GRE, field of the non-label switching network, including an MPLS label of the MPLS VPN, ahead of the NSH field. formatting a generic routing encapsulation, GRE, field of the non-label switching network ahead of the NSH field; and formatting an MPLS label of the MPLS VPN as a context header in the NSH field, or formatting a generic routing encapsulation, GRE, field of the non-label switching network, including an MPLS label of the MPLS VPN, ahead of the NSH field.