Chapter 12. Configuration for NAT

Table of Contents
Basic information
Configuring ProFTPD
Configuring Linux

Contributed by Tobias Ekbom

Basic information

A NAT is a system that acts like a proxy, but on "packet level". When a computer on your local network connects to a computer on the Internet, the NAT replaces the "from" information of packets with it's own address, making your local network invisible to the Internet.

For server systems, NAT can improve security and enable multiple servers to be accessed as a single IP.

This is done by allowing certain ports forwarded "inwards" to the local network. However, the part of the FTP protocol known as "Passive" mode is not by default compatible with NAT solutions. But NAT functionality is possible with ProFTPD from versions 1.2rc2, and this document shows you how.

For details on NAT configuration, read the Linux IP-masq HOWTO ( or search for information concerning your OS of choice.