I’ve looked through the OpenSprinkler code, and I don’t see anything that requires IPv6. I’m running the latest firmware on my RPI, and both IPv4 and IPv6 work perfectly. If you are just running “netstat -a” and seeing that OpenSprinkler is listening only on TCP6, then that seems to be more of a netstat display issue, as it is indeed listening on both IPv6 and IPv4 (at least on my RPI it is like this).