DA-681 Linux
Managing Communications
3-14
NAT Example
The IP address of all packets leaving LAN1 are changed to
192.168.3.127
(you will need to load the
module
ipt_MASQUERADE
):
#ehco 1 > /proc/sys/net/ipv4/ip_forward
#modprobe ipt_MASQUERADE
#iptables –t nat –A POSTROUTING –o eth0 –j MASQUERADE
Enabling NAT at Bootup
In most real world situations, you will want to use a simple shell script to enable NAT when the DA-681-LX
boots up. The following script is an example.
#!/bin/bash
# If you put this shell script in the /home/nat.sh
# Remember to chmod 744 /home/nat.sh
# Edit the rc.local file to make this shell startup automatically.
# vi /etc/rc.local
# Add a line in the end of rc.local /home/nat.sh
EXIF= “eth0” #This is an external interface for setting up a valid IP address.
EXNET= “192.168.4.0/24” #This is an internal network address.
# Step 1. Insert modules.
# Here 2> /dev/null means the standard error messages will be dump to null device.
modprobe ip_tables 2> /dev/null
modprobe ip_nat_ftp 2> /dev/null
modprobe ip_nat_irc 2> /dev/null
modprobe ip_conntrack 2> /dev/null
modprobe ip_conntrack_ftp 2> /dev/null
modprobe ip_conntrack_irc 2> /dev/null
# Step 2. Define variables, enable routing and erase default rules.
PATH=/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin
export PATH
echo “1” > /proc/sys/net/ipv4/ip_forward
