I’ve noticed on the RUTX11 running firmware version 00.07.02.7, using WiFi WAN (set up as per https://youtu.be/INGKWNqnZZ0)…
The WWAN interface won’t take any notice when setting a custom DNS.
Network > Interfaces > WWAN > Advanced Settings > Use Custom DNS Servers > Set as CloudFlare 220.127.116.11 and 18.104.22.168
The weird thing is, my MOB1S1A1 interface will use the custom DNS entries which are applied to the WWAN interface (this shouldn’t happen) but the WWAN interface won’t use them! As soon as I remove the custom DNS entries from the WWAN interface, the mobile interface returns to the default carrier DNS.
It seems like there is a bug - the custom DNS entries aren’t corresponding to the correct interface, despite being set for a specific interface.
I have managed to replicate this behaviour even after a factory reset, following the YouTube video above, and then applying custom DNS to the WWAN interface.
Hoping it can be resolved in a firmware update!