For my networking course, we are assigned some labs that require using a Wireshark, a free packet sniffer. These labs have forced me to start learning some basic commands in Terminal. I am currently running Mac OS X 10.11.
To get one's IP address, assuming en1 to be what you want:
ipconfig getifaddr en1
To find your DNS address:
To flush the DNS cache:
sudo killall -HUP mDNSResponder