nat-vm

#!/bin/bash


function show_usage() {
    echo "Basic usage: $0 [-i <iface>] [-d] <vm_ip>"
    echo "Example: $0 -i eth0 192.168.56.10"
    echo "default interface: eth0"
    echo "-d = remove configuration"
    exit 0
}

remove="0"

# argument parsing
# see: https://stackoverflow.com/questions/192249/how-do-i-parse-command-line-arguments-in-bash
POSITIONAL=()
while [[ $# -gt 0 ]] ; do
    key="$1"
    case $key in
        -h)
        show_usage
        ;;
        -i)
        argiface="$2"
        shift # past argument
        shift # past value
        ;;
        -d)
        remove="1"
        shift # past argument
        ;;
        *)    # unknown option
        POSITIONAL+=("$1") # save it in an array for later
        shift # past argument
        ;;
    esac
done
set -- "${POSITIONAL[@]}" # restore positional parameters

iface=eth0
if [[ "x$argiface" != "x" ]]; then
    iface="$argiface"
fi

vm_ip="${POSITIONAL[0]}"
[[ -z $vm_ip ]] && show_usage

if [[ "x$remove" == "x0" ]] ; then
    sudo bash -c 'echo 1 > /proc/sys/net/ipv4/ip_forward'
    sudo iptables -I FORWARD -s "$vm_ip" -j ACCEPT
    sudo iptables -I FORWARD -d "$vm_ip" -j ACCEPT
    sudo iptables -A POSTROUTING -t nat -o "$iface" -j MASQUERADE
else
    sudo iptables -D POSTROUTING -t nat -o "$iface" -j MASQUERADE
    sudo iptables -D FORWARD -d "$vm_ip" -j ACCEPT
    sudo iptables -D FORWARD -s "$vm_ip" -j ACCEPT
    # do not remove forwading by default
    # just in case it is used for something else
    #sudo bash -c 'echo 1 > /proc/sys/net/ipv4/ip_forward'
fi