FP3+ R 0.21: "Private DNS" is not always working (DoH or DoT)

• /e/ version: 0.21-r-20220113156964-dev-FP3
• Device model(s): FP3+ (Upgraded camera modules)
• Device rooted: No

Summary

• If I set the "DNS" and "Private DNS" settings for some DNS providers with DoH and DoT it is not possible to connect to the internet.

The problem

• Settings > Network and Internet > DNS > Set DNS to use: Enter the IP address
• Settings > Network and Internet > Private DNS > Private DNS provider hostname: Enter the hostname

1. Internet not working:

• DNS: 5.1.66.255
• Private DNS: dot.ffmuc.net or doh.ffmuc.net ("Couldn't connect")
• Link: https://ffmuc.net/wiki/doku.php?id=knb:dohdot#android_9
• ...
• DNS: 208.67.222.222
• Private DNS: doh.opendns.com ("Couldn't connect")
• Link: https://support.opendns.com/hc/en-us/articles/360038086532-Using-DNS-over-HTTPS-DoH-with-OpenDNS

2. Internet working:

• DNS: 1.1.1.1
• Private DNS: 1dot1dot1dot1.cloudflare-dns.com
• Link: https://blog.cloudflare.com/enable-private-dns-with-1-1-1-1-on-android-9-pie/
• ...
• DNS: 8.8.8.8
• Private DNS: dns.google
• Link: https://developers.google.com/speed/public-dns/docs/dns-over-tls
• ...
• DNS: 9.9.9.9
• Private DNS: dns.quad9.net
• Link: https://www.quad9.net/news/blog/enable-private-dns-using-quad9-on-android-9/

It should be possible to connect via DoH or DoT to Freifunk München (dot.ffmuc.net or doh.ffmuc.net) or to OpenDNS (doh.opendns.com) or to other DNS providers with DoH or DoT.

Technical informations

Relevant logs (adb logcat)

Relevant screenshots

Solutions

Workaround

• Workaround is to use a provider which you don't like: E. g. Google, etc.

Possible fixes

• I think it should be possible to enter a full URL into the "Private DNS" field. It's not possible to save the changes when I enter https://...