After further digging through the code, I can see one way that the OpenSprinkler firmware might be listening on IPv6 only. If you check the contents of the file /proc/sys/net/ipv6/bindv6only and it is a “1”, then the OpenSprinkler code would need to bind to IPv4 and IPv6 separately, which I don’t see it doing. This very possibly could lead to an IPv6 only situation. But if the value of bindv6only is a “0”, which it should be in most situations, then the linux kernel takes care of mapping IPv4 packets in to the IPv6 space, and so the single binding is all that is needed for both IPv4 and IPv6 traffic.
So in summary, if you type the following:
cat /proc/sys/net/ipv6/bindv6only
and you get a 0 back, then your installation will work for both IPv4 and IPv6.
I hope this helps…