Coredns in CrashLoopBackOff (kubernetes 1.11)
I had the same problem and needed to allow several ports in my firewall: 22, 53, 6443, 6783, 6784, 8285.
I copied the rules from an existing healthy cluster. Probably only 6443, shown above as the target port for the coredns service, is required for this error and the others are for other services I run in my cluster.
With Ubuntu this was uncomplicated firewall
ufw allow 22/tcp # allowed for ssh, included in case you had firewall disabled altogetherufw allow 6443ufw allow 53ufw allow 8285ufw allow 6783ufw allow 6784