User guide

LTE TDD B2268H

User Guide

8 Network Address Translation (NAT)

Issue 01 (2014-01-15)

8 Network Address Translation (NAT)

8.1 Overview

NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address of a

host in a packet, for example, the source address of an outgoing packet, used within one

network to a different IP address known within another network.

8.1.1 What You Need To Know

The following terms and concepts may help as you read this chapter.

Inside/Outside and Global/Local

Inside/outside denotes where a host is located relative to the LTE Device, for example, the

computers of your subscribers are the inside hosts, while the web servers on the Internet are the

outside hosts.

Global/local denotes the IP address of a host in a packet as the packet traverses a router, for

example, 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.

NAT

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.

Port Forwarding

A port forwarding set is a list of inside (behind NAT on the LAN) servers, for example, web or

FTP, that you can make visible to the outside world even though NAT makes your whole inside

network appear as a single computer to the outside world.

Finding Out More

See Section 9.5 for advanced technical information on NAT.