Note: For VCs with single IP, they share the same DMZ & Virtual servers; for VCs with multiple
IPs, each VC cab set DMZ and Virtual servers. Furthermore, for VCs with multiple IPs, they can
define the Address Mapping rules; for VCs with single IP, since they have only one IP, there is no
need to individually define the Address Mapping rule.
7.3.1 What NAT Does
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. 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.
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7.3.2 How NAT Works
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