Where to find DNS configuration on OS X

To lists manual hosts:

cat /etc/hosts

To list all the resolvers:

scutil --dns

On OS X, /etc/resolv.conf (a symlink to ../var/run/resolv.conf) is not typically used:

cat /etc/resolv.conf
# macOS Notice
# This file is not consulted for DNS hostname resolution, address
# resolution, or the DNS query routing mechanism used by most
# processes on this system.
# To view the DNS configuration used by this system, use:
#   scutil --dns
#   dns-sd(1), scutil(8)
# This file is automatically generated.

On OS X, the DNS resolver may be overwritten for particular LTDs by creating files in /etc/resolver:

cat /etc/resolver/testing
port 53
search_order 1

DNS resolution order

Based on this, apps and ping use the system resolver. dig, nslookup, and host do not.

How to query a specific DNS server

Useful for confirming DNS is configured correctly.

dig <host> +noall +answer <dns_server>