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propagated to other hosts through RIP broadcasts. If you choose No, this route is kept private
and is not included in the RIP broadcasts.
When you are done making changes, click on
SAVE
to save your changes,
DELETE
to delete
the rule with the parameters you set,
BACK
to return to the previous screen or
CANCEL
to
discard changes.
NAT
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.
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 addresses to
globally unique ones required for communication with hosts on other networks. It replaces the
original IP source address (and TCP or UDP source port numbers for Many-to-One and Many-
to-Many Overload NAT mapping) in each packet and then forwards it to the Internet. The
ROUTER keeps track of the original addresses and port numbers so incoming reply packets
can have their original values restored.
NAT Mapping Types
NAT supports five types of IP/port mapping. They are:
One-to-One
– In One-to-One mode, the TC3162 EVM maps one local IP address to one
global IP address.
Many-to-One
– In Many-to-One mode, the TC3162 EVM maps multiple local IP addresses to
one global IP address.
Many-to-Many Overload
– In Many-to-Many Overload mode, the TC3162 EVM maps multiple
local IP addresses to shared global IP addresses.
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