Moxa Technologies 331 User Manual download pdf (Page 44)

Moxa C Programmable RTU Controllers Managing Communications

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# iptables –A INPUT –i eth0 –p all –m mac -–mac-source 01:02:03:04:05:06 –j DROP

NOTE: In Example 7, remember to issue the command #modprobe ipt_mac first to load module ipt_mac.

NAT

NAT (Network Address Translation) protocol translates IP addresses used on one network to different IP

addresses used on another network. One network is designated the inside network and the other is the outside

network. Typically, the RTU controller connects several devices on a network, maps local inside network

addresses to one or more global outside IP addresses, and un-maps the global IP addresses on incoming

packets back into local IP addresses.

NOTE

Click on the following links for more information about iptables and NAT:

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

-HOWTO.html

NAT Example

The IP address of LAN1 is changed to 192.168.127.254 (you will need to load the module ipt_MASQUERADE):

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

2. #modprobe ip_tables

3. #modprobe iptable_filter

4. #modprobe ip_conntrack

5. #modprobe iptable_nat

6. #modprobe ipt_MASQUERADE

7. #iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to-source 192.168.127.254

8. #iptables -t nat -A POSTROUTING -o eth0 -s 192.168.127.0/24 -j MASQUERADE

Enabling NAT at Bootup

In most of the situations, you will want to use a simple shell script to enable NAT when the 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

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Moxa Technologies 331 User Manual Page 44