Power line communication (PLC) is one of the key method of communication for electrical systems due to its advantage in using existing power line infrastructure. It can be used for emerging smart grid applications such as the advanced metering infrastructure (AMI) where embedded smart meters report electricity usage autonomously. To enable AMI over PLC, however, a suitable networking protocol is required. RPL is the IETF standard of IPv6 routing protocol for low power and lossy networks, designed mainly to support multihop wireless networking between resource constrained embedded devices. To understand the performance and potentials of RPL over PLC, this work implements a RPL-based network architecture over a multihop PLC network, and evaluates the performance of RPL over PLC through extensive real-world testbed experiments using 18 PLC devices. The result shows that the standard RPL with OF0 is not suitable for PLC network, and motivates a necessity of a new path selection algorithm.