I have just set up a DNS server for my own network, and many guides online suggest to make sure that port forwarding on port 53 is not enabled.
The thing that is not clear to me is this: should I configure this at the router level or at the firewall level? If I should do this on the firewall, how would I go about doing this on an Ubuntu Server 12.04?
My home network has a few clients, an ESXi server and a home router. One of the VMs inside ESXi is the DNS server (running on Ubuntu Server 12.04) which is used to handle local DNS requests but is also configured as to forward requests for external IPs to Google's DNS servers.