Moxa EM-1220-LX [38/57] Nat example

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

Example 4: Drop TCP packets from 192.168.1.25.

# iptables –A INPUT –i eth0 –p tcp –s 192.168.1.25 –j DROP

Example 5: Drop TCP packets addressed for port 21.

# iptables –A INPUT –i eth0 –p tcp --dport 21 –j DROP

Example 6: Accept TCP packets from 192.168.0.24 to the EM-1240-LX’s port 137, 138, 139

# iptables –A INPUT –i eth0 –p tcp –s 192.168.0.24 --dport 137:139 –j ACCEPT

Example 7: Log TCP packets that visit EM-1240-LX’s port 25.

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

Example 8: Drop all packets from MAC address 01:02:03:04:05:06.

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

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):

First load the following device drivers:

x_tables.ko

xt_multiport.ko

xt_MARK.ko

xt_tcpudp.ko

ip_tables.ko

ip_nat.ko

iptable_nat.ko

ipt_MASQUERADE.ko

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

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

#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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