Nat Definitions - Atlantis Land Web Share 111U User Manual

8.1.1 NAT Definitions

Inside/outside denotes where a host is located relative to the ADSL Router, for
example, the computers of your subscribers are the inside hosts, while the web
servers on the Internet are the outside hosts.
Global/local denotes the IP address of a host in a packet as the packet traverses a
router, for example, 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 in 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
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.
8.1.2 What NAT Does
In the simplest form, NAT changes the source IP address in a packet received from a
subscriber (the inside local address) to another (the inside global address) before
forwarding the packet to the 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. In addition, you can designate servers, for example, a web server
and a telnet server, on your local network and make them accessible to the outside
world. With no servers defined, the ADSL Router filters out all incoming inquiries, thus
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