There are many kinds of control networks which have been used in various non-IP network areas, such as BA (Building Automation), FA (Factory Automation) and PA (Process Automation). Recently, many control network technologies have been introducing IP (Internet Protocol) and Ethernet for cost/capabilities benefits. IPv6, in particular, can be a driving force for the movement. However, it can influence entire architectures of control network technologies because it can invalidate implicit premises, i.e. closed networks, which have contributed to the dependability of the systems. This paper review the issues of control networks when introducing IP, and shows that IPv6 is crucial.