Arch Linux

itarill

Member

Registered: 2020-06-03

Posts: 59

[Solved] FallbackDNS not utilized

I used to have pihole and unbound configured, but as I played around with it and some other containers I mangled my connectivity somehow. A btrfs rollback later, I am troubleshooting connectivity issues with pihole/unbound removed.

my /etc/systemd/resolved.conf contains the following:

DNS=127.0.0.1 ::1
FallbackDNS=1.1.1.1 8.8.8.8 9.9.9.10 2606:4700:4700::1111 2620:fe::10 2001:4860:4860::8888

If I change DNS to 8.8.8.8 (for instance), I have normal connectivity. If I leave it as is, there is no domain name resolution. I'd love to know why the fallback DNS are not made use of.

I have also added

DNSStubListener=yes

I have normal connectivity in the network (no change), so I figured that this is the root cause for this arch machine. Thanks.

Last edited by itarill (2024-08-02 09:21:19)

-thc

Member

Registered: 2017-03-15

Posts: 766

Re: [Solved] FallbackDNS not utilized

This is mostly a misconception based on the name of that setting.

"FallbackDNS" does not work as a secondary DNS entry in case the first/primary is unreachable but as a fallback for systemd-resolved if neither "DNS" is specified nor any DNS servers are acquired through DHCP:

This setting is hence only used if no other DNS server information is known.

itarill

Member

Registered: 2020-06-03

Posts: 59

Re: [Solved] FallbackDNS not utilized

Thanks, this was useful. Are the DNS servers in the list "DNS=" queried in hierarchy (i.e. according to their respective order in the list)?

Last edited by itarill (2024-08-02 07:33:19)

-thc

Member

Registered: 2017-03-15

Posts: 766

Re: [Solved] FallbackDNS not utilized

The documentation doesn't mention any processing order. But resolved chooses one of them as "Current DNS server".

Last edited by -thc (2024-08-02 07:39:47)