Moxa Technologies 331 User Manual download pdf (Page 42)

Moxa C Programmable RTU Controllers Managing Communications

4-8

Use the lsmod command to check if the ip_tables module has already been loaded in the Moxa RTU unit. Use

the modprobe command to insert and enable the module.

Use the following command to load the modules (iptable_filter, iptable_mangle, iptable_nat):

#modprobe iptable_filter

NOTE

IPTABLES plays the role

of packet filtering or NAT. Be careful

when setting up the IPTABLES rules. If the rules

are not correct, remote hosts that

are connected via a LAN or PPP may deny access. It is stro

ngly recommended

to use the serial co

nsole to set up the IPTABLES.

Click on the following links for more information about iptables.

http://www.linuxguruz.com/iptables/

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

-filtering-HOWTO.html

Since the IPTABLES command is very complex, illustrating the IPTABLES syntax is divided into three categories:

Observe and erase chain rules, Define policy rules, and Append or delete rules.

Observe and Erase Chain Rules

Usage:

# iptables [-t tables] [-L] [-n]

-t tables: Table to manipulate (default: ‘filter’); example: nat or filter.

-L [chain]: List List all rules in selected chains. If no chain is selected, all chains are listed.

-n: Numeric output of addresses and ports.

# iptables [-t tables] [-FXZ]

-F: Flush the selected chain (all the chains in the table if none is listed).

-X: Delete the specified user-defined chain.

-Z: Set the packet and byte counters in all chains to zero.

Examples:

# iptables -L -n

In this example, since we do not use the -t parameter, the system uses the default ‘filter’ table. Three chains

are included: INPUT, OUTPUT, and FORWARD. INPUT chains are accepted automatically, and all connections

are accepted without being filtered.

#iptables –F

#iptables –X

#iptables –Z

Define Policy for Chain Rules

Usage:

# iptables [-t tables] [-P] [INPUT, OUTPUT, FORWARD, PREROUTING, OUTPUT, POSTROUTING]

[ACCEPT, DROP]

-P: Set the policy for the chain to the given target.

INPUT: For packets coming into the Moxa RTU.

OUTPUT: For locally-generated packets.

FORWARD: For packets routed out through the Moxa RTU.

PREROUTING: To alter packets as soon as they come in.

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