destroy NAT gateway on OSX

destroy_gw.sh

#!/bin/bash
# All these steps look excessive but address
# network instability issues created by not doing them

gwdev=`netstat -nr | grep default | awk '{ print $6 }' | head -1`

if [ -z "$gwdev" ]; then
gwdev=en1
fi

killall natd
/sbin/ipfw delete 100 divert natd ip from any to any via $gwdev
sysctl -w net.inet.ip.forwarding=0
ifconfig $gwdev down
ifconfig en0 down
route delete default -interface bridge0 -ifscope bridge0
ifconfig bridge0 172.20.0.1 delete
ifconfig bridge0 deletem en0
ifconfig bridge0 destroy
ifconfig en0 up
ifconfig $gwdev up