Another way to enable IP forwarding.

[Jonathan Simms]

We know of two ways to enable IP forwarding, the echo 1 > /proc/sys/net/ipv4/ip_forward and to edit the /etc/sysctl.conf file. There is another way- you can add FOWARD_IPV4=yes to the /etc/sysconfig/network file.

[url]http://tldp.org/LDP/solrhe/Securing-Optimizing-Linux-RH-Edition-v1.3/chap9sec93.html[/url]

[Kayla Smith]

Cool.

I also learned recently that if you want the "1" value to get from the /etc/sysctl.conf file to take effect right away, you don't have to "service network restart", there's actually a command called "sysctl -p".

[Jonathan Simms]

I was bored today so I wrote a two scripts that will turn IP Forward on, one is in bash and the other in Python.


[code]#!/bin/bash

one=$(grep ip_forward /etc/sysctl.conf | awk '{ print $3 }')

if [ $UID != 0 ]
then
echo "Must be super user" 1>&2
exit 1
fi

if [ $one == 1 ]
then
echo "IP Forwarding is already on" 1>&2
elif [ $one == 0 ]
then
sed -i 's/ip_forward = 0/ip_forward = 1/' /etc/sysctl.conf
sysctl -p > /dev/null
echo "IP Forwarding is now on"
fi
[/code]
[code]#!/usr/bin/python

import fileinput
from os import popen, getuid
from sys import exit

zero = 'net.ipv4.ip_forward = 0'
one = 'net.ipv4.ip_forward = 1'
file = open('/etc/sysctl.conf')

if getuid() != 0:
print "Must be super user"
exit(1)

for lines in file:
if zero in lines:
for line in fileinput.FileInput('/etc/sysctl.conf', inplace=1):
line = line.replace(zero, one)
print line.strip()
print "IP Forwarding is now on"
popen('sysctl -p')
elif one in lines:
print "IP Forwading is already on"

file.close()
[/code]

[Rich Simms]

Nice! - Rich