# Shorewall Version 4

Tom
Eastep
2007
2009
Thomas M. Eastep

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.

## Introduction

Shorewall version 4.0 represented a substantial shift in direction for Shorewall. Up until then

- Shorewall had been written entirely in Bourne Shell.

- Shorewall had run the `iptables` utility to add each Netfilter rule.

Shorewall version 4.0 offered you a choice. You could continue to use the existing shell-based implementation or you could use a new implementation of the Shorewall compiler written in the Perl programming language. The new compiler:

- had a small disk footprint

- was very fast.

- generateed a firewall script that uses `iptables-restore`; so the script was very fast.

- generated better and more consistent error messages.

- did a much more thorough job of checking the configuration to avoid run-time errors.

- supported creating either Ipv4 or Ipv6 firewalls (Shorewall 4.2.4 and later).

Both compilers could be installed on your system and you could use whichever one suited you in a particular case.

## Shorewall 4.4

Shorewall 4.4 discontinues the availability of the legacy shell-based compiler. All users must migrate to the perl-based compiler before or during an upgrade to Shorewall version 4.4. We highly recommend that current users of the shell-based compiler migrate before upgrading to 4.4 so that both compilers are available during the migration.

Shorewall 4.4 contains four packages:

- Shorewall - Everything needed to create an IPv4 firewall.

- Shorewall-lite- Can run scripts generated by Shorewall on another system.

- Shorewall6 - The utilities for creating and operating an Ipv6 firewall. Requires Shorewall.

- Shorewall6-lite - Ipv6 equivalent of Shorewall Lite. Can run scripts generated by Shoreall on another system.

## Prerequisites for using the Shorewall Version 4.2/4.4 Perl-based Compiler

- Perl (I use Perl 5.8.10 but other 5.8 versions should work fine).

  If you want to be able to use DNS names in your Shorewall6 configuration files, then Perl 5.10 is required together with the Perl Socket6 module.

- Perl Cwd Module

- Perl File::Basename Module

- Perl File::Temp Module

- Perl Getopt::Long Module

- Perl Carp Module

- Perl FindBin Module

- Perl Scalar::Util Module

Please note that there are additional requirements if you plan to install and use Shorewall6.

## Incompatibilities Introduced in the Shorewall Version 4 Perl-based Compiler

The Shorewall Perl-based compiler is not 100% compatible with the Shorewall shell-based version. See this document for details.