I have two SIMs for my hotspot, both of which do IPv6, so I enable it and it works (I use “NAT6” on the LAN when using mobile data).
But if I switch to a WAN w/o IPv6 (i.e., many hotel Ethernets) while the IPv6 toggle is on, the WAN side still thinks it’s got an IPv6 address, so the LAN side continues to advertise (RD?) the ULA for the NAT6 (fd15:: ) so devices on the LAN think they can still route IPv6, and fail. See below for a screenshot of what it looks like after switching from an IPv6 dual-stack connection to an IPv4-only connection.
I guess- I’m not exactly sure- but perhaps when Interfaces change and IPv6 is enabled, to tear it down and let it come back up if the WAN advertises IPv6? I can fix this by toggling IPv6 off then disconnecting/reconnecting each client device, but that’s pretty unwieldy.