D-Link DI-206 manual How NAT Works

DI-206 ISDN Remote Router

Network Address Port Translation (NAPT) is a subset of NAT where many local IP addresses and their TCP/UDP port numbers are translated to a single global IP address and it’s TCP/UDP port number. In this document, the term NAT will refer to both NAT and NAPT unless otherwise stated.

NAT can work in conjunction with DHCP. Thus, if both are enabled and properly configured, the DHCP server in the DI-206 will assign local IP addresses to computers on your network.

How NAT Works

In the most common NAT configuration, your network uses local IP addresses that are not valid on the Internet. Internet (global) IP addresses are unique, with no two devices have the same IP address. The local IP addresses can be freely assigned to computers on your network by your network administrator (within guidelines defined later in this chapter and in Appendix B, “IP Concepts”). This can be done manually or by using DHCP. The ISDN port on the router is assigned a globally unique IP Address that IS valid on the Internet, since it will be sending and receiving data directly to the Internet and is therefore part of it. Please study the example diagram below carefully.

Single

Global

IP Address

176.220.22.1

ISDN

PortWAN

Router NAT

Translator

LAN

Port

Local IP LAN

192.168.100.1

192.168.100.2 192.168.100.3 192.168.100.4 192.168.100.5

Please note that in the above diagram, the Gateway IP address settings for the local PC’s needs to be set to 192.168.100.1, the LAN IP address of the router.

NAT manipulates the IP addresses in packet headers on a one-to-one basis. An outgoing data packet (a packet originating from a computer on the local LAN and destined for a computer outside the private network) will have its IP address translated as shown below.

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