Moxa W321-LX [42/80] Iptables

Moxa W341-LX [42/80] Iptables
W321/341 Linux
-3
/etc/nsswitch.conf
This file defines the sequence to resolve the IP address by using /etc/hosts file or /etc/resolv.conf.
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 W321/341 support 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
chainworks 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
MASQUERADEa special form for SNAT. If one host can connect to i
nternet, then other computers that
connect to this host can connect to the Internet even if these computers 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.

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