niczsoft

Had you ever need of simple routing, like sharing your connection to other computer?

I had :) so here is a script which turns my laptop into a router, simple configuration, one command, to run it save the script as router.sh

#!/bin/bash

#configuration
IF_LOC=eth0
IP_LOC=192.168.67
IF_NET=wlan0

#script
IF_NET=$(ifconfig $IF_NET | awk '/inet/ {print $2}' | grep -o '[0-9]*\.[0-9]*\.[0-9]*')

#connect
iptables-save > /dev/shm/old_routes
ifconfig $IF_LOC inet $IP_LOC.1
ip route add $IP_LOC.0/24 dev $IF_LOC src $IP_LOC.1
iptables -t nat -A POSTROUTING -s $IF_NET.0/24 -j MASQUERADE

if ip route | grep $IP_LOC.1 >/dev/null
then
  #message
  clear
  echo "Enter this information in connected machines:"
  echo "IP address : $IP_LOC.2-254"
  echo "Netmask    : 255.255.255.0"
  echo "Gateway    : $IP_LOC.1"
  echo "DNS        : $(echo -n $(awk '/^nameserver/ {print $2}' /etc/resolv.conf))"
  echo ""
  echo "Press ENTER to continue."
  read

  #monitor connection
  iftop -i $IF_LOC

else
  echo "Error setting up network"
fi

#disconnect
ip route del $IP_LOC.0/24 dev $IF_LOC
ifconfig $IF_LOC down
iptables-restore < /dev/shm/old_routes
rm /dev/shm/old_routes

#end

and give execute rights to the script:

chmod +x router.sh

now just run it:

sudo ./router.sh

Script will show configuration of new created network

Enter this information in connected machines:
IP address : 192.168.67.2-254
Netmask    : 255.255.255.0
Gateway    : 192.168.67.1
DNS        : 217.172.224.160 89.228.6.21

Press ENTER to continue.

and start monitor its traffic, to quit routing hit q or CTRL+C

It is simplest way to start sharing internet I know off