For some reason, Ubuntu server 18.04 does not start with a valid ethernet connection on my newly acquired, an oldie but goodie, Dell R710 server. After some searching around this solution at tecmint that works for me.

sudo netplan generate 
sudo vim /etc/netplan/01-netcfg.yaml 
ifconfig -a # find the ethernet name, mine is eno1
# this will auto config using DHCP

network:
 version: 2
 renderer: networkd
 ethernets:
   eno1:
     dhcp4: yes
     dhcp6: yes

sudo netplan apply
ifconfig -a # should now show IP on eno1