User Manual

Chapter 10 Network Address Translation
NBG-418N v2 User’s Guide
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incoming inquiries, thus preventing intruders from probing your network. For more information on IP
address translation, refer to RFC 1631, The IP Ne two rk Addre ss Tra nslato r (NAT).
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 in each packet and then forwards it to the Internet. The NBG-418N v2 keeps track of the original
addresses and port numbers so incoming reply packets can have their original values restored. The
following figure illustrates this.
Fig ure 75 How NAT Works
10.3 Ge ne ra l NAT Sc re e n
Use this screen to enable NAT and set a default server. Click Ne twork > NAT to open the Ge ne ra l screen.
Fig ure 76 Network > NAT > General