IPFirewall is the default firewall for Mac OSX and FreeBSD. Use the ipfw command tool to define firewall rules for your computer.
This shell script creates my firewall rules when I am using insecure networks in my professional work. The script configuring firewall logging and create rules to block traffic on network all interfaces except loopback interface and outbound traffic for HTTP, HTTPS, SSH, SMTP, NTP and DNS.
#!/bin/sh
sudo ipfw -q flush
if [ "$1" = "on" ]; then
sudo sysctl -w net.inet.ip.fw.verbose=2 > /dev/null
sudo ipfw -q add allow ip from me to any via lo0
sudo ipfw -q add allow tcp from me to any 80 keep-state out
sudo ipfw -q add allow tcp from me to any 443 keep-state out
sudo ipfw -q add allow tcp from me to any 22 keep-state out
sudo ipfw -q add allow tcp from me to any 993 keep-state out
sudo ipfw -q add allow tcp from me to any 25 keep-state out
sudo ipfw -q add allow udp from me to any 123 keep-state out
sudo ipfw -q add allow udp from me to any 53 keep-state out
sudo ipfw -q add deny log all from any to any
echo "Firewall is activated"
else
sudo sysctl -w net.inet.ip.fw.verbose=0 > /dev/null
echo "Firewall is disabled"
fi
