PLANET ADN-4000 - Manual (Page 49)

WAN side. When the response comes back, NAT translates the destination address (the
inside global address) back to the inside local address before forwarding it to the
original inside host. Note that the IP address (either local or global) of an outside host is
never changed.
The global IP addresses for the inside hosts can be either static or dynamically assigned
by the ISP. You may also designate servers, such as a Web server and a telnet server, on
your local network and make them accessible to the outside world. With no servers
defined, your ROUTER filters out all incoming inquiries, thus preventing intruders
from probing your network. For more information on IP address translation, refer to
RFC 1631, The IP Network Address Translator (NAT).
Inside/outside indicates where a host is located relative to the ROUTER. The
computers hosts of your LAN are inside, while the Web servers on the Internet are
outside.
Global/local indicates the IP address of a host in a packet as the packet traverses a
router. The local address refers to the IP address of a host when the packet is in the local
network, while the global address refers to the IP address of the host when the same
packet is traveling in the WAN side.
Note that inside/outside refers to the location of a host, while global/local refers to the
IP address of a host used in a packet. Thus, an inside local address (ILA) is the IP
address of an inside host of a packet when the packet is still in the local network, while
an inside global address (IGA) is the IP address of the same inside host when the packet
is on the WAN side.
The following table summarizes this information.
ITEM DESCRIPTION
Inside This refers to the host on the LAN.
Outside This refers to the host on the WAN.
Local This refers to the packet address (source or destination) as the
packet travels on the LAN.
Global This refers to the packet address (source or destination) as the
packet travels on the WAN.
How NAT Works
Each packet has two addresses – a source address and a destination address. For
outgoing packets, the ILA is the source address on the LAN, and the IGA is the source
address on the WAN. For incoming packets, the ILA is the destination address on the
LAN, and the IGA is the destination address on the WAN. NAT maps private (local) IP
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