checkys.net does this, but it's not an uptime monitoring system, it is a connectivity checking system. You can specify ip6 or ip4 or just ip if you don't care.

checkys.net does this, but it's not an uptime monitoring system, it is a connectivity checking system. You can specify ip6 or ip4 or just ip if you don't care. Some people have both A and AAAA on the same name, while others do not and most uptime monitoring systems are not technical enough to care or know the difference.