There used to be an elegant simplicity to listing nameservers in resolv.conf.
Is there any reason for the systemd-redolved service? Am I correct that, without that, resolv.conf becomes a static DNS configuration file? The only difference I can perceive is that the service offers different setting on different interfaces (which is also a potential problem). Moreover, what on earth does 127.0.0.53 point to? Bind still works from 127.0.0.1:53.
Secondly, I am confused by the options afforded by NetworkManager (aside from the fact that it should be “networkmanager.”)
There is “automatic” which presumable relies on the router’s settings.
Then there is “automatic (only addresses)” which means NOT automatic. Name resolution from the IPAs entered in “DNS Servers.” Correct? I notice that resolv.conf doesn’t change.
Next is “link-local.” I have no clue what that means.
Next is “manual.” What is the difference between manual and automatic (only addresses)?
To tell the truth, resolv.conf is basically obsolete as it no longer fits modern challenges.
Name resolution is not limited to DNS, there’s also LLMNR and mDNS, and DNS traffic is not limited to plain UDP as it can also be encrypted using DoT and verified with DNSSEC.
Different DNS servers may have their own priority and scope to utilize with split DNS, and may be required to change dynamically based on active Ethernet/Wi-Fi/VPN/etc. connections.
In addition, DNS caching can noticeably improve performance for name resolution.
All of the above can be configured with NetworkManager and systemd-resolved.
Use DHCP/DHCPv6/SLAAC to configure IP/routes/DNS/etc.
Use DHCP/DHCPv6/SLAAC to configure IP/routes, but ignore DNS announced by those services.
Use zeroconf to configure IP and expect LLMNR/mDNS for name resolution.