Moxa Technologies EM-1240-LX user manual NAT Example, Enabling NAT at Bootup

EM-1240-LX User’s Manual Configuring EM-1240-LX

NAT

NAT (Network Address Translation) protocol translates IP addresses used on one network into different IP addresses used on another network. One network is designated the inside network and the other is the outside network. Typically, the EM-1240-LX connects several devices on a network and maps local inside network addresses to one or more global outside IP addresses, and remaps the global IP addresses on incoming packets back into local IP addresses.

NOTE Click the following link for more information about iptables and NAT:

http://www.netfilter.org/documentation/HOWTO/NAT-HOWTO.html

NAT Example

The IP addresses of all packets leaving LAN1 are changed to 192.168.3.127 (you will need to load the module ipt_MASQUERADE):

1.#echo 1 > /proc/sys/net/ipv4/ip_forward

2.#iptables -t nat –A POSTROUTING –o eth0 –j SNAT --to-source 192.168.3.127

or

3.#iptables –t nat –A POSTROUTING –o eth0 –j MASQUERADE

Enabling NAT at Bootup

In most real world situations, you should use a simple shell script to enable NAT when the EM-1240-LX boots up, as indicated by the following:

1.setting iptables

2.iptables-save > /home/xxx.file (xxx.file is the user defined file name)

3.vi /etc/rc

4.	Append	echo 1 > /proc/sys/net/ipv4/ip_forward
5.	Append	iptables-restore /home/xxx.file (xxx.file is the user defined file name)

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