Ethernet has been used for connecting hosts in the area of high performance-per-cost PC clusters. Although L2 Ethernet topology is limited to a tree structure, various routing algorithms on topologies suitable for parallel processing can be employed by applying IEEE 802.1Q VLAN technology. However, communication library used in current PC clusters does not always support VLANs, so the current design of VLAN-based routing method cannot be applied for such PC clusters. In this study, we propose a switch-tagged VLAN methodology to flexibly set the route of frames on such PC clusters. Since each host does not need to process VLAN tags, the proposed method has advantages in both simple host configuration and high portability. Evaluation results using NAS Parallel Benchmarks showed that performance of topologies supported by the proposed method was comparable with that of an ideal 1-switch (full crossbar) network in the case of a 16-host PC cluster.