setup_tap.sh

#!/bin/bash
# Creates a tap interface: tap0
# Modifies the routing table so that everything goes through Tap0 except stuff going to the DNS server.

#if [ "$#" -lt 1 ] ; then
#	echo "Please indicate the DNS server's IP."
#	exit 0
#elif [ "$#" -gt 1 ] ; then
#	echo "Too many arguments: Please only indicate the DNS server's IP."
#	exit 1
#fi

iptap=10.10.10.1

#create a tap interface
openvpn --mktun --dev tap0

#bring it up
ip link set tap0 up

#give it an ip address
ip addr add $iptap dev tap0

#Limits the MSS to the interface's MTU
#iptables -I OUTPUT -p tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu

#get the default gateway (IP address of the router)
#DEFR=$(netstat -rn | grep "^0.0.0.0 " | awk '{print $2}')

#delete it
#route del default gw $DEFR

#assign tap0 as the default gateway: all traffic to 8.8.8.8 goes into tap0 first
route add 8.8.8.8 gw $iptap

#show the IP routing table
netstat -rn