#!/bin/sh

####################################
#                                  #
# host -> gateway -> INTERNET      #
#                                  #
####################################

# Ethernet card in host computer
ECARDINHOST=eth0
# Ethernet card in gateway computer (connects to host)
ECARTINGW_2HOST=eth0
# Ethernet card in gateway computer (connects to Internet)
ECARDINGW_2INTERNET=eth1


## Settings for host<->gateway network

# Netmask
NETMASK=255.255.255.0
# IP address for gateway
IP_GW=192.168.50.2
# IP address for host
IP_HOST=192.168.50.1


if [ "$#" -eq "0" ]; then
    echo -e "Usage:\n\t$0 [--gateway|--host]\n"
    exit 0
elif [ "$#" -eq "1" ]; then
    case "$1" in
        "--gateway")
            #checking internet connection
            ping -W 5 -c 1 ya.ru
            if [ "$?" -ne "0" ]; then
                echo 'No Internet connection! Aborting!!!'
                exit 1
            fi
            # enable packet forwarding
            sudo -u root -s "echo 1 > /proc/sys/net/ipv4/ip_forward"
            sudo ifconfig $ECARTINGW_2HOST $IP_GW netmask $NETMASK
            sudo iptables -t nat -A POSTROUTING -o $ECARDINGW_2INTERNET -j MASQUERADE
            echo 'Add this lines to /etc/resolv.conf in host computer (not in gateway!):'
            echo
            cat /etc/resolv.conf
            echo
            exit 0
            ;;
        "--host")
            sudo ifconfig $ECARDINHOST $IP_HOST netmask $NETMASK
            sudo route add default gw $IP_GW
            echo 'Add lines from gateway resolv.com to host resolv.conf'
            echo 'Do not forget say "sudo route del default gw 192.168.50.2"!'
            exit 0
            ;;
    esac
fi