Wr3000, Port wireless dsl/cable router – ParkerVision WR3000 User Manual

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WR3000

4-Port Wireless DSL/Cable Router

9.1 NAT Overview - Continued

9.1.2 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. Although you can make

designated servers on the LAN accessible to the outside world, it is strongly recommended that

you attach those servers to the DMZ port instead. If you do not deﬁ ne any servers (for Many-to-

One and Many-to-Many Overload mapping), NAT offers the additional beneﬁ t of ﬁ rewall

protection. With no servers deﬁ ned, your WR3000 Wireless Router ﬁ lters 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).

9.1.3 How NAT Works
Each packet has two addresses - a source address and a destination address. For outgoing

packets, the ILA (Inside Local Address) is the source address on the LAN, and the IGA (Inside

Global Address) 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 WR3000 Wireless Router keeps track of the original

addresses and port numbers so incoming reply packets can have their original values restored.

The following ﬁ gure illustrates this.