Using a Raspberry PI as a Router and Wifi hotspot with a firewall for your internal LAN or household network is now possible. The Wifi hotspot can function as a hotspot for guests. This can be more secure then the cheap nasty routers supplied by your ISP with hard coded passwords.
This post will show you how to install DNS with bind9 and DHCP on Ubuntu 16.04. We will end up with a full blown bind9 DNS with an integrated DHCP server. If you are a home user and your network has grown such that you are tired of using all static IP addresses and having to configure the /etc/hosts files by hand, then use the great tool dnsmasq. See my How to set up dnsmasq. Dnsmasq is so much simpler to setup and maintain than bind9, you should think about using it.
DNS with bind9 and DHCP on Ubuntu 16.04 also works on a Raspberry PI 3 running the Ubuntu Image.