add_masquerade.sh

add_masquerade.sh

#!/bin/bash

interface=ipsec_bridge
target_ip="192.168.2.100"
cidr_ip=$(ip addr show "$interface" | grep 'inet ' | awk '{print $2}')
network=$(ipcalc "$cidr_ip"  | grep "Network:" | awk '{print $2}')

function add_masquerade {
    iptables -t nat -C POSTROUTING -s "$network" -j SNAT --to "$target_ip" || {
        iptables -t nat -I POSTROUTING 1 -s "$network" -j SNAT --to "$target_ip"
    }
}

function clear_masquerade {
    iptables -t nat -C POSTROUTING -s "$network" -j SNAT --to "$target_ip" && {
        iptables -t nat -D POSTROUTING -s "$network" -j SNAT --to "$target_ip"
    }
}

echo "Prepare to add NAT source network from $network to $target_ip"
add_masquerade
echo "Insert a source NAT rule in front of POSTROUTING chain...."
echo "Done!"

# Install signal handlers
trap "clear_masquerade" SIGINT SIGTERM

sleep infinity &
# wait for SIGINT or SIGTERM
wait
echo "Gracefully shutdown!"