Moxa DA-662A-I-8-LX [36/63] Iptables

DA-662A Series Software Managing Communications

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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”.

DA-662A series 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 it 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.