Huawei Technologies Futurewei Technologies KDDI Corporation China Telecom China Mobile China Mobile Cisco Systems Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent topological or service based instructions. A segment can further be associated with a set of network resources used for executing the instruction. Such a segment is called resource-aware segment. Resource-aware Segment Identifiers (SIDs) may be used to build SR paths with a set of reserved network resources. In addition, a group of resource-aware SIDs may be used to build SR based virtual underlay networks, which has customized network topology and resource attributes required by one or a group of customers and/or services. Such virtual networks are the SR instantiations of Virtual Transport Networks (VTNs). This document describes a suggested use of resource-aware SIDs to build SR based VTNs.