Novell LINUX ENTERPRISE SERVER 10 - INSTALLATION AND ADMINISTRATION 11-05-2007 Installation Manual page 836

nat
This table defines any changes to the source and target addresses of packets. Using
these functions also allows you to implement masquerading, which is a special
case of NAT used to link a private network with the Internet.
mangle
The rules held in this table make it possible to manipulate values stored in IP
headers (such as the type of service).
Figure 43.1 iptables: A Packet's Possible Paths
These tables contain several predefined chains to match packets:
PREROUTING
This chain is applied to incoming packets.
INPUT
This chain is applied to packets destined for the system's internal processes.
FORWARD
This chain is applied to packets that are only routed through the system.
OUTPUT
This chain is applied to packets originating from the system itself.
818 Installation and Administration
PREROUTING
incoming packet
mangle
INPUT
mangle
Routing
filter
FORWARD
Processes
mangle
in the local
system
filter
OUTPUT
Routing
mangle
nat
filter
POSTROUTING
mangle
outgoing packet
nat
nat