Moxa KM-2430-T [33/52] Enabling nat at bootup

ioPAC RTU Software RTU Communications

4-8

Enabling NAT at Bootup

In most real world situations, use a simple shell script to enable NAT when the ioPAC RTU controller 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.d/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=‘192.168.126.0/24’ #This is an internal network address.

1. Insert modules.

# Here 2> /dev/null means the standard error messages will be dump to null device.

modprobe nf_tables 2> /dev/null

modprobe nf_conntrack 2> /dev/null

modprobe nf_conntrack_ftp 2> /dev/null

modprobe nf_conntrack_irc 2> /dev/null

modprobe iptable_nat 2> /dev/null

modprobe nf_nat_ftp 2> /dev/null

modprobe nf_nat_irc 2> /dev/null

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

/bin/iptables -F

/bin/iptables -X

/bin/iptables -Z

/bin/iptables -F -t nat

/bin/iptables -X -t nat

/bin/iptables -Z -t nat

/bin/iptables -P INPUT ACCEPT

/bin/iptables -P OUTPUT ACCEPT

/bin/iptables -P FORWARD ACCEPT

/bin/iptables -t nat -P PREROUTING ACCEPT

/bin/iptables -t nat -P POSTROUTING ACCEPT

/bin/iptables -t nat -P OUTPUT ACCEPT

3. Enable IP masquerade.