AI Protection, DNS Filtering, Global Filtering - I don't think there's a firmware glitch because of Items 5 and 7 below. But just in case .......
RT-AC68U
I decided to re-check the DNS Filtering after the .53 flash.
Prior to flashing with .53, I had DNS Filtering set to ON and Global set to No Filtering, ( using the Client list as required).
After the .53 flash, I changed Global Filter Mode to Router and found I couldn't initially access the Internet.
WAN DNS Servers 1 and 2 are set to my malicious-domain-blocking Raspberry Pi at 192.168.1.10. LAN-DHCP DNS is blank.
On testing:
1. Global= Router, Internet = BLOCKED
2. Global= Custom 1 = 192.168.1.10, Internet = BLOCKED
3. Global= Router, device in Client List set to (Custom) 192.168.1.10, Internet = BLOCKED
4. Global= Router, device in Client List set to Router, Internet = BLOCKED
5. Global= Router, device in Client List set to Custom 1= 8.8.8.8 or any pre-listed eg OpenDNS, Internet= ACCESS
6. Global= No Filtering, device in Client set to Router, Internet = ACCESS
7. But when I changed WAN DNS to, say, 8.8.8.8 (instead of 192.168.1.10) (and left Global Filter Mode as Router), I could access the Internet.
So the glitch appears down to my having 192.168.1.10 (the Raspberry Pi DNS server) in my WAN DNS when Global Filtering Mode is set to Router (or internal Custom device).
As I say, this is not even an inconvenience for me: I don't need DNS Filtering, and I could always go back to No Filtering and use the Client List. I'm only concerned that there shouldn't be a bug.
SOLVED As indicated, not a bug. Problem is that the the internal DNS server - 192.168.1.10 - needs to be listed in the Client List in DNS Filtering under NO FILTERING, otherwise I guess an infinite loop is set up: the Global Filter says ROUTER and, unless otherwise specified, that includes the local DNS server, whose external DNS address is, in my case, the 2 OpenDNS servers. So, unless it's listed as NO FILTERING in the Client List, it gets sent back to the Router instead of out to the public DNS server.