Fresh Ubuntu Server install can reach the internet but not resolve local hostnames

A manually run `dhcpcd` process changing the behavior suggests that more than one component may be managing the interface, but it does not prove that DHCP failed to provide DNS. Check the active link with `networkctl status eth0`, confirm that systemd-resolved is running, and inspect `/etc/resolv.conf` to see whether it points to the local resolved stub. Make sure there is only one network manager controlling the interface and that any `.network` configuration has DNS use enabled.

The absence of a desktop environment makes the GNOME/NetworkManager explanation unlikely. A fresh client can still expose an existing DNS problem simply because it is the first machine being tested closely. Since the DNS server itself reports temporary failures for internal names, I would inspect the local BIND zone, zone-file syntax, reload logs, permissions, and whether the server is authoritative for the expected internal domain before changing the new client's configuration.

Separate the failure into three cases: no name resolution, a name resolving to the wrong address, or a correct address that cannot be reached. `resolvectl query hostname.example` and `resolvectl status` can show which DNS server is being contacted and whether the search domain is installed. From another host, query the DNS server directly with something like `dig @DNS_SERVER hostname`. If that direct query fails, changing Netplan or systemd-networkd on the client will not fix it.

The later testing points strongly toward the local DNS server rather than the new Ubuntu installation. If the DNS/DHCP server itself cannot resolve local names, while internet names still work, the local zone or forwarding configuration may be broken. Check that the zone containing your internal hostnames is loaded, that its records are present, and that the server is listening and answering on the LAN interface. Also verify that the DHCP server is advertising the intended DNS address and search domain.