Moxa Technologies 331 User Manual download pdf (Page 40)

UC-7112-LX Plus Software User’s Manual Managing Communications

4-7

IPTABLES

IPTABLES is an administrative tool for setting up, maintaining, and inspecting the Linux kernel’s

IP packet filter rule tables. Several different tables are defined, with each table containing built-in

chains and user-defined chains.

Each chain is a list of rules that apply to a certain type of packet. Each rule specifies what to do

with a matching packet. A rule (such as a jump to a user-defined chain in the same table) is called

a “target.”

The UC-7112-LX Plus supports 3 types of IPTABLES table: Filter tables, NAT tables, and

Mangle tables:

A. Filter Table—includes three chains:

INPUT chain

OUTPUT chain

FORWARD chain

B. NAT Table—includes three chains:

PREROUTING chain—transfers the destination IP address (DNAT)

POSTROUTING chain—works after the routing process and before the Ethernet device

process to transfer the source IP address (SNAT)

OUTPUT chain—produces local packets

sub-tables

Source NAT (SNAT)—changes the first source packet IP address

Destination NAT (DNAT)—changes the first destination packet IP address

MASQUERADE—a special form for SNAT. If one host can connect to Internet, then

other computers that connect to this host can connect to the Internet when the computer

does not have an actual IP address.

REDIRECT—a special form of DNAT that re-sends packets to a local host independent

of the destination IP address.

C. Mangle Table—includes two chains

PREROUTING chain—pre-processes packets before the routing process.

OUTPUT chain—processes packets after the routing process.

It has three extensions—TTL, MARK, TOS.

The following figure shows the IPTABLES hierarchy.

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Moxa Technologies 331 User Manual Page 40