Shorewall IPv6 Support

Tom 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”.

2009/06/05


Table of Contents

Overview
Prerequisites
Packages
IPv4/IPv6 Interaction
DISABLE_IPV6
TC_ENABLED
KEEP_RT_TABLES
6TO4
Shorewall6 Differences from Shorewall
Installing IPv6 Support
More information about IPv6

Caution

This article applies to Shorewall 4.3 and later. If you are running a version of Shorewall earlier than Shorewall 4.3.5 then please see the documentation for that release.

Overview

Beginning with Shorewall 4.2.4, support for firewalling IPv6 is included as part of Shorewall.

Prerequisites

In order to use Shorewall with IPv6, your firewall must meet the following prerequisites:

  1. Kernel 2.6.24 or later.

  2. Iptables 1.4.0 or later (1.4.1.1 is strongly recommended)

  3. If you wish to include DNS names in your IPv6 configuration files, you must have Perl 5.10 and must install the Perl Socket6 library.

Packages

Shorewall IPv6 support introduced two new packages:

  1. Shorewall6. This package provides /sbin/shorewall6 which is the IPv6 equivalent of /sbin/shorewall. /sbin/shorewall only handles IPv4 while /sbin/shorewall6 handles only IPv6.. Shorewall6 depends on Shorewall. The Shorewall6 configuration is stored in /etc/shorewall6.

  2. Shorewall6 Lite. This package is to IPv6 what Shorewall Lite is to IPv4. The package stores its configuration in /etc/shorewall6-lite. As with Shorewall Lite, Shorewall6 Lite usually requires no configuration changes on the firewall system.

IPv4/IPv6 Interaction

IP connections are either IPv4 or IPv6; there is no such thing as a mixed IPv4/6 connecton. IPv4 connections are controlled by Shorewall (or Shorewall-lite); IPv6 connections are controlled by Shorewall6 (or Shorewall6-lite). Starting and stopping the firewall for one address family has no effect on the other address family.

As a consequence, there is very little interaction between Shorewall and Shorewall6.

DISABLE_IPV6

An obvious area where the configuration of Shorewall affects Shorewall6 is the DISABLE_IPV6 setting in /etc/shorewall/shorewall.conf. When configuring Shorewall6, you will want to set DISABLE_IPV6=No and restart Shorewall or Shorewall-lite.

TC_ENABLED

Another area where their configurations overlap is in traffic shaping; the tcdevices and tcclasses files do exactly the same thing in both Shorewall and Shorewall6. Consequently, you will have TC_ENABLED=Internal in Shorewall or in Shorewall6 and TC_ENABLED=No in the other product. Also, you will want CLEAR_TC=No in the configuration with TC_ENABLED=No.

Regardless of which product has TC_ENABLED=Internal:

  • IPv4 packet marking is controlled by /etc/shorewall/tcrules

  • IPv6 packet marking is controlled by /etc/shorewall6/tcrules

KEEP_RT_TABLES

Multi-ISP users will need to be aware of this one. When there are entries in the providers file, Shorewall normally installs a modified /etc/iproute2/rt_tables during shorewall start and shorewall restart and restores a default file during shorewall stop. Setting KEEP_RT_TABLES=Yes in shorewall.conf(5) stops Shorewall (Shorewall lite) from modifying /etc/iproute2/rt_tables.

Shorewall6 is also capable of modifying /etc/iproute2/rt_tables in a similar way.

Our recommendation to Multi-ISP users is to:

These setting allow Shorewall to control the contents of /etc/iproute2/rt_tables.

6TO4

If you are using a 6to4 tunnel for your IPv6 connectivity, you need an entry in /etc/shorewall/tunnels.

#TYPE    ZONE    GATEWAY        GATEWAY
#                               ZONE
6to4     net
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE

Shorewall6 Differences from Shorewall

Configuring and operating Shorewall6 is very similar to configuring Shorewall with some notable exceptions:

No NAT

In Shorewall6, there is no NAT of any kind (Netfilter6 doesn't support any form of NAT). Most people consider this to be a giant step forward.

When an ISP assigns you an IPv6 address, you are actually assigned an IPv6 prefix (similar to a subnet). A 64-bit prefix defines a subnet with 4 billion hosts squared (the size of the IPv4 address space squared). Regardless of the length of your prefix, you get to assign local addresses within that prefix.

Default Zone Type

The default zone type in Shorewall6 is ipv6. It is suggested that you specify ipv6 in the TYPE column of /etc/shorewall6/zones and a type of ipv4 in /etc/shorewall/zones; that way, if you run the wrong utility on a configuration, you will get an instant error.

Interface Options

The following interface options are available in /etc/shorewall6/interfaces:

blacklist

Same as in Shorewall

bridge

Same as in Shorewall

dhcp

Interface is assigned by IPv6 DHCP or the firewall hosts an IPv6 DHCP server on the interface.

maclist

Same as in Shorewall

nosmurfs

Checks the source IP address of packets arriving on the interface and drops packets whose SOURCE address is:

  • An IPv6 multicast address

  • The subnet-router anycast address for any of the global unicast addresses assigned to the interface.

  • An RFC 2526 anycast address for any of the global unicast addresses assigned to the interface.

optional

Same as in Shorewall

routeback

Same as in Shorewall

sourceroute[={0|1}]

Same as in Shorewall

tcpflags

Same as in Shorewall

mss=mss

Same as in Shorewall

forward[={0|1}]

Override the setting of IP_FORWARDING in shorewall6.conf with respect to how the system behaves on this interface. If 1, behave as a router; if 0, behave as a host.

Host Options

The following host options are available in /etc/shorewall6/hosts:

blacklist

Same as in Shorewall

maclist

Same as in Shorewall

routeback

Same as in Shorewall

tcpflags

Same as in Shorewall

Specifying Addresses

Anywhere that an address or address list follows a colon (":"), the address or list may be enclosed in angled brackets ("<" and ">") to improve readability.

Example (/etc/shorewall6/rules):

#ACTION        SOURCE              DEST                        PROTO          DEST
#                                                                             PORT(S)
ACCEPT         net                 $FW:<2002:ce7c:92b4::3>     tcp            22

When the colon is preceeded by an interface name, the angle brackets are required. This is true even when the address is a MAC address in Shorewall format.

Example (/etc/shorewall6/rules):

#ACTION        SOURCE                            DEST          PROTO          DEST
#                                                                             PORT(S)
ACCEPT         net:wlan0:<2002:ce7c:92b4::3>     tcp                         22
Stopped State

When Shorewall6 or Shorewall6 Lite is in the stopped state, the following traffic is still allowed.

  • Traffic with a multicast destination IP address (ff00::/8).

  • Traffic with a link local source address (ff800::/8)

  • Traffic with a link local destination address.

Multi-ISP

The Linux IPv6 stack does not support balancing (multi-hop) routes. Hence, neither the balance option in shorewall6-providers(5) nor USE_DEFAULT_RT=Yes in shorewall6.conf(5) is supported.

/sbin/shorewall6 and /sbin/shorewall6-lite Commands

Several commands supported by /sbin/shorewall and /sbin/shorewall-lite are not supported by /sbin/shorewall6 and /sbin/shorewall6-lite:

  • hits

  • ipcalc

  • iprange

Macros

The Shorewall6 package depends on Shorewall-common for application macros. Only certain address-family specific macros such as macro.AllowICMPs are included in Shorewall6. As a consequence, /usr/share/shorewall/ is included in the default Shorewall6 CONFIG_PATH.

Installing IPv6 Support

You will need at least the following packages:

  • Shorewall 4.3.5 or later.

  • Shorewall6 4.3.5 or later.

You may also with to install Shorewall6-lite 4.3.5 or later on your remote firewalls to allow for central IPv6 firewall administration.

More information about IPv6

I strongly suggest that you read the Linux IPv6 HOWTO. The 6to4 Tunnels page also includes instructions for setting up your first IPv6 environment.

In addition to the Linux IPv6 HOWTO, I have found the following two books to be useful:

  • IPv6 Essentials, Silvia Hagen, 2002, O'Reilly Media, Inc, ISBN 0-596-00125-8.

    O'Reilly published a second edition of this book in 2006.

  • IPV6 Theory, Protocol, and Practice, Second Edition, Pete Loshin, 2004, Morgan-Kaufmann Publishers, IBSN 1-55860-820-9