Determine IPv6 for a connected device

Greetings,

Today, we tweaked one or two IPv6 settin" gs on my RS300, and we noticed that it was already malfunctioning. We were unsure whether "RIPng" was a necessary setting.

However, we have often observed that IPv6 stops working: that is, for client devices on the inside of my LAN on a normal ISP connection, they lose their unique globally-routed IPv6 assignments and Network Prefix. There is no particular reason for this that we've been able to discern.

The Netgear router is typically configured to "Auto Config" under the Advanced-> IPv6 settings. But it also often loses the "Router IPv6 address on WAN" and/or "Router IPv6 address on LAN" for no reason. Our workaround for this is usually to tweak the "Auto Detect" setting to "Auto Detect" or off/then on, or something else, briefly "Apply" and then revert to the settings which had originally worked. 

Our ISP appears to not have implemented DHCPv6. Therefore the DHCPv6 settings were non-functional. However, SLAAC is typically functional, and it is the usual way we obtain the Network Prefix delegated from ISP. 

Furthermore, if anyone knows a way to easily do introspection on IPv6 and IPv4 WAN addresses, please let us know. Formerly, we used English Wikipedia, or Meta or Commons while logged out, but that doesn't work due to their privacy restrictions now. "whatismyipaddress dot com" is clogged with nearly malicious ads and streaming video that bombard us as soon as we visit that site. We cannot find any IPv6-capable tools on dynu.com, which is a really good site otherwise!