Configure systemd-resolved to use a specific DNS nameserver for a given domain
Use case
Given
- I use a VPN to connect to my work network
- I'm on a Linux computer that uses systemd-resolved
- I have a work domain called
example.com example.comis hosted by both public and private DNS nameservers- Both public and private nameservers claim to be authoritative for
example.com - There are no public hosts in
example.com - The public resolvers for
example.comresolve all queries to a parked hosting webpage - The private resolvers for
example.comcontain all correct DNS records for private hosts
I need to
- Resolve private hosts in
example.comwhen connected to VPN
(Note that this should also work for pointing DNS-blocked domains at different, non-blocked nameservers)
Solution
systemd-resolved now has the ability to specify nameservers for specific domains. Until recently this was not the case, systemd-resolved leaned on NetworkManager, which used dnsmasq for this purpose.
If you were already doing something like this to accomplish this task, first undo all of that. We're not going to use NetworkManager/dnsmasq.
In your systemd-resolved config, which for me is at /etc/systemd/resolved.conf (Fedora), make sure you have this (assuming example.com private nameservers are 10.0.0.1 and 10.0.0.2)
[Resolve]
DNS=10.0.0.1 10.0.0.2
Domains=~example.com
Note the tilde, that makes systemd-resolved do something special. According to the man page:
Specified domain names may optionally be prefixed with "~". In this case they do not define a search path, but preferably direct DNS queries for the indicated domains to the DNS servers configured with the system DNS= setting (see above), in case additional, suitable per-link DNS servers are known.
Restart systemd-resolved and you should be in business.
