Networking on mac can be tricky, the same applies to NAT. If we want our mac to act as NAT we need:

  1. Enable forwarding

sudo sysctl -w net.inet.ip.forwarding=1

  1. Create a file with our NAT rules for eg nat_rules with our configuration

nat on en0 from en1 to any -> (en0)

  1. Start PF via pfctl
sudo pfctl -d                     # stop pfctl
sudo pfctl -F all -f ./nat_rules  # flush all rules and load new ones
sudo pfctl -e                     # start pfctl