This script quickly switches between different dns servers...

setdns

#!/bin/bash

usage="$(basename "$0") sets the DNS for the wifi network to one of the following:

[-n]ative: sets to local DNS
[-g]oogle: sets to google DNS
[-t]unlr:  sets to tunlr DNS

[-h]elp prints this help message.
"

native="empty"
google="8.8.8.8 8.8.4.4"
tunlr="45.33.81.76 45.33.12.13"


while getopts ":hngt" opt; do
  case $opt in
    h)
      echo "$usage"
      ;;
    n)
      dns=$native
      ;;
    g)
      dns=$google
      ;;
    t)
      dns=$tunlr
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      exit 1
      ;;
  esac
done

if $( networksetup -setdnsservers Wi-Fi $dns ); then
  echo "Set DNS to" $dns
else
  echo "Failed to set DNS"
fi